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# Docker Registry HTTP API V2
## Introduction
The _Docker Registry HTTP API_ is the protocol to facilitate distribution of
images to the docker engine. It interacts with instances of the docker
registry, which is a service to manage information about docker images and
enable their distribution. The specification covers the operation of version 2
of this API, known as _Docker Registry HTTP API V2_.
While the V1 registry protocol is usable, there are several problems with the
architecture that have led to this new version. The main driver of this
specification these changes to the docker the image format, covered in
docker/docker#8093. The new, self-contained image manifest simplifies image
definition and improves security. This specification will build on that work,
leveraging new properties of the manifest format to improve performance,
reduce bandwidth usage and decrease the likelihood of backend corruption.
For relevant details and history leading up to this specification, please see
the following issues:
- [docker/docker#8093](https://github.com/docker/docker/issues/8093)
- [docker/docker#9015](https://github.com/docker/docker/issues/9015)
- [docker/docker-registry#612](https://github.com/docker/docker-registry/issues/612)
### Scope
This specification covers the URL layout and protocols of the interaction
between docker registry and docker core. This will affect the docker core
registry API and the rewrite of docker-registry. Docker registry
implementations may implement other API endpoints, but they are not covered by
this specification.
This includes the following features:
- Namespace-oriented URI Layout
- PUSH/PULL registry server for V2 image manifest format
- Resumable layer PUSH support
- V2 Client library implementation
While authentication and authorization support will influence this
specification, details of the protocol will be left to a future specification.
Relevant header definitions and error codes are present to provide an
indication of what a client may encounter.
#### Future
There are features that have been discussed during the process of cutting this
specification. The following is an incomplete list:
- Immutable image references
- Multiple architecture support
- Migration from v2compatibility representation
These may represent features that are either out of the scope of this
specification, the purview of another specification or have been deferred to a
future version.
### Use Cases
For the most part, the use cases of the former registry API apply to the new
version. Differentiating use cases are covered below.
#### Image Verification
A docker engine instance would like to run verified image named
"library/ubuntu", with the tag "latest". The engine contacts the registry,
requesting the manifest for "library/ubuntu:latest". An untrusted registry
returns a manifest. Before proceeding to download the individual layers, the
engine verifies the manifest's signature, ensuring that the content was
produced from a trusted source and no tampering has occured. After each layer
is downloaded, the engine verifies the digest of the layer, ensuring that the
content matches that specified by the manifest.
#### Resumable Push
Company X's build servers lose connectivity to docker registry before
completing an image layer transfer. After connectivity returns, the build
server attempts to re-upload the image. The registry notifies the build server
that the upload has already been partially attempted. The build server
responds by only sending the remaining data to complete the image file.
#### Resumable Pull
Company X is having more connectivity problems but this time in their
deployment datacenter. When downloading an image, the connection is
interrupted before completion. The client keeps the partial data and uses http
`Range` requests to avoid downloading repeated data.
#### Layer Upload De-duplication
Company Y's build system creates two identical docker layers from build
processes A and B. Build process A completes uploading the layer before B.
When process B attempts to upload the layer, the registry indicates that its
not necessary because the layer is already known.
If process A and B upload the same layer at the same time, both operations
will proceed and the first to complete will be stored in the registry (Note:
we may modify this to prevent dogpile with some locking mechanism).
### Changes
The V2 specification has been written to work as a living document, specifying
only what is certain and leaving what is not specified open or to future
changes. Only non-conflicting additions should be made to the API and accepted
changes should avoid preventing future changes from happening.
This section should be updated when changes are made to the specification,
indicating what is different. Optionally, we may start marking parts of the
specification to correspond with the versions enumerated here.
<dl>
<dt>2.0.1</dt>
<dd>
<ul>
<li>Added support for immutable manifest references in manifest endpoints.</li>
<li>Deleting a manifest by tag has been deprecated.</li>
<li>Specified `Docker-Content-Digest` header for appropriate entities.</li>
<li>Added error code for unsupported operations.</li>
</ul>
</dd>
<dt>2.0</dt>
<dd>
This is the baseline specification.
</dd>
</dl>
## Overview
This section covers client flows and details of the API endpoints. The URI
layout of the new API is structured to support a rich authentication and
authorization model by leveraging namespaces. All endpoints will be prefixed
by the API version and the repository name:
/v2/<name>/
For example, an API endpoint that will work with the `library/ubuntu`
repository, the URI prefix will be:
/v2/library/ubuntu/
This scheme provides rich access control over various operations and methods
using the URI prefix and http methods that can be controlled in variety of
ways.
Classically, repository names have always been two path components where each
path component is less than 30 characters. The V2 registry API does not
enforce this. The rules for a repository name are as follows:
1. A repository name is broken up into _path components_. A component of a
repository name must be at least two lowercase, alpha-numeric characters,
optionally separated by periods, dashes or underscores. More strictly, it
must match the regular expression `[a-z0-9]+(?:[._-][a-z0-9]+)*` and the
matched result must be 2 or more characters in length.
2. The name of a repository must have at least two path components, separated
by a forward slash.
3. The total length of a repository name, including slashes, must be less the
256 characters.
These name requirements _only_ apply to the registry API and should accept a
superset of what is supported by other docker ecosystem components.
All endpoints should support aggressive http caching, compression and range
headers, where appropriate. The new API attempts to leverage HTTP semantics
where possible but may break from standards to implement targeted features.
For detail on individual endpoints, please see the [_Detail_](#detail)
section.
### Errors
Actionable failure conditions, covered in detail in their relevant sections,
are reported as part of 4xx responses, in a json response body. One or more
errors will be returned in the following format:
{
"errors:" [{
"code": <error identifier>,
"message": <message describing condition>,
"detail": <unstructured>
},
...
]
}
The `code` field will be a unique identifier, all caps with underscores by
convention. The `message` field will be a human readable string. The optional
`detail` field may contain arbitrary json data providing information the
client can use to resolve the issue.
While the client can take action on certain error codes, the registry may add
new error codes over time. All client implementations should treat unknown
error codes as `UNKNOWN`, allowing future error codes to be added without
breaking API compatibility. For the purposes of the specification error codes
will only be added and never removed.
For a complete account of all error codes, please see the _Detail_ section.
### API Version Check
A minimal endpoint, mounted at `/v2/` will provide version support information
based on its response statuses. The request format is as follows:
GET /v2/
If a `200 OK` response is returned, the registry implements the V2(.1)
registry API and the client may proceed safely with other V2 operations.
Optionally, the response may contain information about the supported paths in
the response body. The client should be prepared to ignore this data.
If a `401 Unauthorized` response is returned, the client should take action
based on the contents of the "WWW-Authenticate" header and try the endpoint
again. Depending on access control setup, the client may still have to
authenticate against different resources, even if this check succeeds.
If `404 Not Found` response status, or other unexpected status, is returned,
the client should proceed with the assumption that the registry does not
implement V2 of the API.
### Pulling An Image
An "image" is a combination of a JSON manifest and individual layer files. The
process of pulling an image centers around retrieving these two components.
The first step in pulling an image is to retrieve the manifest. For reference,
the relevant manifest fields for the registry are the following:
field | description |
----------|------------------------------------------------|
name | The name of the image. |
tag | The tag for this version of the image. |
fsLayers | A list of layer descriptors (including tarsum) |
signature | A JWS used to verify the manifest content |
For more information about the manifest format, please see
[docker/docker#8093](https://github.com/docker/docker/issues/8093).
When the manifest is in hand, the client must verify the signature to ensure
the names and layers are valid. Once confirmed, the client will then use the
tarsums to download the individual layers. Layers are stored in as blobs in
the V2 registry API, keyed by their tarsum digest.
#### Pulling an Image Manifest
The image manifest can be fetched with the following url:
```
GET /v2/<name>/manifests/<reference>
```
The `name` and `reference` parameter identify the image and are required. The
reference may include a tag or digest.
A `404 Not Found` response will be returned if the image is unknown to the
registry. If the image exists and the response is successful, the image
manifest will be returned, with the following format (see docker/docker#8093
for details):
{
"name": <name>,
"tag": <tag>,
"fsLayers": [
{
"blobSum": <tarsum>
},
...
]
],
"history": <v1 images>,
"signature": <JWS>
}
The client should verify the returned manifest signature for authenticity
before fetching layers.
#### Pulling a Layer
Layers are stored in the blob portion of the registry, keyed by tarsum digest.
Pulling a layer is carried out by a standard http request. The URL is as
follows:
GET /v2/<name>/blobs/<tarsum>
Access to a layer will be gated by the `name` of the repository but is
identified uniquely in the registry by `tarsum`. The `tarsum` parameter is an
opaque field, to be interpreted by the tarsum library.
This endpoint may issue a 307 (302 for <HTTP 1.1) redirect to another service
for downloading the layer and clients should be prepared to handle redirects.
This endpoint should support aggressive HTTP caching for image layers. Support
for Etags, modification dates and other cache control headers should be
included. To allow for incremental downloads, `Range` requests should be
supported, as well.
### Pushing An Image
Pushing an image works in the opposite order as a pull. After assembling the
image manifest, the client must first push the individual layers. When the
layers are fully pushed into the registry, the client should upload the signed
manifest.
The details of each step of the process are covered in the following sections.
#### Pushing a Layer
All layer uploads use two steps to manage the upload process. The first step
starts the upload in the registry service, returning a url to carry out the
second step. The second step uses the upload url to transfer the actual data.
Uploads are started with a POST request which returns a url that can be used
to push data and check upload status.
The `Location` header will be used to communicate the upload location after
each request. While it won't change in the this specification, clients should
use the most recent value returned by the API.
##### Starting An Upload
To begin the process, a POST request should be issued in the following format:
```
POST /v2/<name>/blobs/uploads/
```
The parameters of this request are the image namespace under which the layer
will be linked. Responses to this request are covered below.
##### Existing Layers
The existence of a layer can be checked via a `HEAD` request to the blob store
API. The request should be formatted as follows:
```
HEAD /v2/<name>/blobs/<digest>
```
If the layer with the tarsum specified in `digest` is available, a 200 OK
response will be received, with no actual body content (this is according to
http specification). The response will look as follows:
```
200 OK
Content-Length: <length of blob>
Docker-Content-Digest: <digest>
```
When this response is received, the client can assume that the layer is
already available in the registry under the given name and should take no
further action to upload the layer. Note that the binary digests may differ
for the existing registry layer, but the tarsums will be guaranteed to match.
##### Uploading the Layer
If the POST request is successful, a `202 Accepted` response will be returned
with the upload URL in the `Location` header:
```
202 Accepted
Location: /v2/<name>/blobs/uploads/<uuid>
Range: bytes=0-<offset>
Content-Length: 0
Docker-Upload-UUID: <uuid>
```
The rest of the upload process can be carried out with the returned url,
called the "Upload URL" from the `Location` header. All responses to the
upload url, whether sending data or getting status, will be in this format.
Though the URI format (`/v2/<name>/blobs/uploads/<uuid>`) for the `Location`
header is specified, clients should treat it as an opaque url and should never
try to assemble the it. While the `uuid` parameter may be an actual UUID, this
proposal imposes no constraints on the format and clients should never impose
any.
If clients need to correlate local upload state with remote upload state, the
contents of the `Docker-Upload-UUID` header should be used. Such an id can be
used to key the last used location header when implementing resumable uploads.
##### Upload Progress
The progress and chunk coordination of the upload process will be coordinated
through the `Range` header. While this is a non-standard use of the `Range`
header, there are examples of [similar approaches](https://developers.google.com/youtube/v3/guides/using_resumable_upload_protocol) in APIs with heavy use.
For an upload that just started, for an example with a 1000 byte layer file,
the `Range` header would be as follows:
```
Range: bytes=0-0
```
To get the status of an upload, issue a GET request to the upload URL:
```
GET /v2/<name>/blobs/uploads/<uuid>
Host: <registry host>
```
The response will be similar to the above, except will return 204 status:
```
204 No Content
Location: /v2/<name>/blobs/uploads/<uuid>
Range: bytes=0-<offset>
Docker-Upload-UUID: <uuid>
```
Note that the HTTP `Range` header byte ranges are inclusive and that will be
honored, even in non-standard use cases.
##### Monolithic Upload
A monolithic upload is simply a chunked upload with a single chunk and may be
favored by clients that would like to avoided the complexity of chunking. To
carry out a "monolithic" upload, one can simply put the entire content blob to
the provided URL:
```
PUT /v2/<name>/blobs/uploads/<uuid>?digest=<tarsum>[&digest=sha256:<hex digest>]
Content-Length: <size of layer>
Content-Type: application/octet-stream
<Layer Binary Data>
```
The "digest" parameter must be included with the PUT request. Please see the
_Completed Upload_ section for details on the parameters and expected
responses.
Additionally, the upload can be completed with a single `POST` request to
the uploads endpoint, including the "size" and "digest" parameters:
```
POST /v2/<name>/blobs/uploads/?digest=<tarsum>[&digest=sha256:<hex digest>]
Content-Length: <size of layer>
Content-Type: application/octet-stream
<Layer Binary Data>
```
On the registry service, this should allocate a download, accept and verify
the data and return the same response as the final chunk of an upload. If the
POST request fails collecting the data in any way, the registry should attempt
to return an error response to the client with the `Location` header providing
a place to continue the download.
The single `POST` method is provided for convenience and most clients should
implement `POST` + `PUT` to support reliable resume of uploads.
##### Chunked Upload
To carry out an upload of a chunk, the client can specify a range header and
only include that part of the layer file:
```
PATCH /v2/<name>/blobs/uploads/<uuid>
Content-Length: <size of chunk>
Content-Range: <start of range>-<end of range>
Content-Type: application/octet-stream
<Layer Chunk Binary Data>
```
There is no enforcement on layer chunk splits other than that the server must
receive them in order. The server may enforce a minimum chunk size. If the
server cannot accept the chunk, a `416 Requested Range Not Satisfiable`
response will be returned and will include a `Range` header indicating the
current status:
```
416 Requested Range Not Satisfiable
Location: /v2/<name>/blobs/uploads/<uuid>
Range: 0-<last valid range>
Content-Length: 0
Docker-Upload-UUID: <uuid>
```
If this response is received, the client should resume from the "last valid
range" and upload the subsequent chunk. A 416 will be returned under the
following conditions:
- Invalid Content-Range header format
- Out of order chunk: the range of the next chunk must start immediately after
the "last valid range" from the previous response.
When a chunk is accepted as part of the upload, a `202 Accepted` response will
be returned, including a `Range` header with the current upload status:
```
202 Accepted
Location: /v2/<name>/blobs/uploads/<uuid>
Range: bytes=0-<offset>
Content-Length: 0
Docker-Upload-UUID: <uuid>
```
##### Completed Upload
For an upload to be considered complete, the client must submit a `PUT`
request on the upload endpoint with a digest parameter. If it is not provided,
the upload will not be considered complete. The format for the final chunk
will be as follows:
```
PUT /v2/<name>/blob/uploads/<uuid>?digest=<tarsum>[&digest=sha256:<hex digest>]
Content-Length: <size of chunk>
Content-Range: <start of range>-<end of range>
Content-Type: application/octet-stream
<Last Layer Chunk Binary Data>
```
Optionally, if all chunks have already been uploaded, a `PUT` request with a
`digest` parameter and zero-length body may be sent to complete and validated
the upload. Multiple "digest" parameters may be provided with different
digests. The server may verify none or all of them but _must_ notify the
client if the content is rejected.
When the last chunk is received and the layer has been validated, the client
will receive a `201 Created` response:
```
201 Created
Location: /v2/<name>/blobs/<tarsum>
Content-Length: 0
Docker-Content-Digest: <digest>
```
The `Location` header will contain the registry URL to access the accepted
layer file. The `Docker-Content-Digest` header returns the canonical digest of
the uploaded blob which may differ from the provided digest. Most clients may
ignore the value but if it is used, the client should verify the value against
the uploaded blob data.
###### Digest Parameter
The "digest" parameter is designed as an opaque parameter to support
verification of a successful transfer. The initial version of the registry API
will support a tarsum digest, in the standard tarsum format. For example, a
HTTP URI parameter might be as follows:
```
tarsum.v1+sha256:6c3c624b58dbbcd3c0dd82b4c53f04194d1247c6eebdaab7c610cf7d66709b3b
```
Given this parameter, the registry will verify that the provided content does
result in this tarsum. Optionally, the registry can support other other digest
parameters for non-tarfile content stored as a layer. A regular hash digest
might be specified as follows:
```
sha256:6c3c624b58dbbcd3c0dd82b4c53f04194d1247c6eebdaab7c610cf7d66709b3b
```
Such a parameter would be used to verify that the binary content (as opposed
to the tar content) would be verified at the end of the upload process.
For the initial version, registry servers are only required to support the
tarsum format.
##### Canceling an Upload
An upload can be cancelled by issuing a DELETE request to the upload endpoint.
The format will be as follows:
```
DELETE /v2/<name>/blobs/uploads/<uuid>
```
After this request is issued, the upload uuid will no longer be valid and the
registry server will dump all intermediate data. While uploads will time out
if not completed, clients should issue this request if they encounter a fatal
error but still have the ability to issue an http request.
##### Errors
If an 502, 503 or 504 error is received, the client should assume that the
download can proceed due to a temporary condition, honoring the appropriate
retry mechanism. Other 5xx errors should be treated as terminal.
If there is a problem with the upload, a 4xx error will be returned indicating
the problem. After receiving a 4xx response (except 416, as called out above),
the upload will be considered failed and the client should take appropriate
action.
Note that the upload url will not be available forever. If the upload uuid is
unknown to the registry, a `404 Not Found` response will be returned and the
client must restart the upload process.
#### Pushing an Image Manifest
Once all of the layers for an image are uploaded, the client can upload the
image manifest. An image can be pushed using the following request format:
PUT /v2/<name>/manifests/<reference>
{
"name": <name>,
"tag": <tag>,
"fsLayers": [
{
"blobSum": <tarsum>
},
...
]
],
"history": <v1 images>,
"signature": <JWS>,
...
}
The `name` and `reference` fields of the response body must match those specified in
the URL. The `reference` field may be a "tag" or a "digest".
If there is a problem with pushing the manifest, a relevant 4xx response will
be returned with a JSON error message. Please see the _PUT Manifest section
for details on possible error codes that may be returned.
If one or more layers are unknown to the registry, `BLOB_UNKNOWN` errors are
returned. The `detail` field of the error response will have a `digest` field
identifying the missing blob, which will be a tarsum. An error is returned for
each unknown blob. The response format is as follows:
{
"errors:" [{
"code": "BLOB_UNKNOWN",
"message": "blob unknown to registry",
"detail": {
"digest": <tarsum>
}
},
...
]
}
#### Listing Image Tags
It may be necessary to list all of the tags under a given repository. The tags
for an image repository can be retrieved with the following request:
GET /v2/<name>/tags/list
The response will be in the following format:
200 OK
Content-Type: application/json
{
"name": <name>,
"tags": [
<tag>,
...
]
}
For repositories with a large number of tags, this response may be quite
large, so care should be taken by the client when parsing the response to
reduce copying.
### Deleting an Image
An image may be deleted from the registry via its `name` and `reference`. A
delete may be issued with the following request format:
DELETE /v2/<name>/manifests/<reference>
For deletes, `reference` *must* be a digest or the delete will fail. If the
image exists and has been successfully deleted, the following response will be
issued:
202 Accepted
Content-Length: None
If the image had already been deleted or did not exist, a `404 Not Found`
response will be issued instead.
## Detail
> **Note**: This section is still under construction. For the purposes of
> implementation, if any details below differ from the described request flows
> above, the section below should be corrected. When they match, this note
> should be removed.
The behavior of the endpoints are covered in detail in this section, organized
by route and entity. All aspects of the request and responses are covered,
including headers, parameters and body formats. Examples of requests and their
corresponding responses, with success and failure, are enumerated.
> **Note**: The sections on endpoint detail are arranged with an example
> request, a description of the request, followed by information about that
> request.
A list of methods and URIs are covered in the table below:
|Method|Path|Entity|Description|
-------|----|------|------------
{{range $route := .RouteDescriptors}}{{range $method := .Methods}}| {{$method.Method}} | `{{$route.Path|prettygorilla}}` | {{$route.Entity}} | {{$method.Description}} |
{{end}}{{end}}
The detail for each endpoint is covered in the following sections.
### Errors
The error codes encountered via the API are enumerated in the following table:
|Code|Message|Description|
-------|----|------|------------
{{range $err := .ErrorDescriptors}} `{{$err.Value}}` | {{$err.Message}} | {{$err.Description|removenewlines}}
{{end}}
{{range $route := .RouteDescriptors}}
### {{.Entity}}
{{.Description}}
{{range $method := $route.Methods}}
#### {{.Method}} {{$route.Entity}}
{{.Description}}
{{if .Requests}}{{range .Requests}}{{if .Name}}
##### {{.Name}}{{end}}
```
{{$method.Method}} {{$route.Path|prettygorilla}}{{if .QueryParameters}}?{{range .QueryParameters}}{{.Name}}={{.Format}}{{end}}{{end}}{{range .Headers}}
{{.Name}}: {{.Format}}{{end}}{{if .Body.ContentType}}
Content-Type: {{.Body.ContentType}}{{end}}{{if .Body.Format}}
{{.Body.Format}}{{end}}
```
{{.Description}}
{{if or .Headers .PathParameters .QueryParameters}}
The following parameters should be specified on the request:
|Name|Kind|Description|
|----|----|-----------|
{{range .Headers}}|`{{.Name}}`|header|{{.Description}}|
{{end}}{{range .PathParameters}}|`{{.Name}}`|path|{{.Description}}|
{{end}}{{range .QueryParameters}}|`{{.Name}}`|query|{{.Description}}|
{{end}}{{end}}
{{if .Successes}}
{{range .Successes}}
###### On Success: {{if .Name}}{{.Name}}{{else}}{{.StatusCode | statustext}}{{end}}
```
{{.StatusCode}} {{.StatusCode | statustext}}{{range .Headers}}
{{.Name}}: {{.Format}}{{end}}{{if .Body.ContentType}}
Content-Type: {{.Body.ContentType}}{{end}}{{if .Body.Format}}
{{.Body.Format}}{{end}}
```
{{.Description}}
{{if .Headers}}The following headers will be returned with the response:
|Name|Description|
|----|-----------|
{{range .Headers}}|`{{.Name}}`|{{.Description}}|
{{end}}{{end}}{{end}}{{end}}
{{if .Failures}}
{{range .Failures}}
###### On Failure: {{if .Name}}{{.Name}}{{else}}{{.StatusCode | statustext}}{{end}}
```
{{.StatusCode}} {{.StatusCode | statustext}}{{range .Headers}}
{{.Name}}: {{.Format}}{{end}}{{if .Body.ContentType}}
Content-Type: {{.Body.ContentType}}{{end}}{{if .Body.Format}}
{{.Body.Format}}{{end}}
```
{{.Description}}
{{if .Headers}}
The following headers will be returned on the response:
|Name|Description|
|----|-----------|
{{range .Headers}}|`{{.Name}}`|{{.Description}}|
{{end}}{{end}}
{{if .ErrorCodes}}
The error codes that may be included in the response body are enumerated below:
|Code|Message|Description|
-------|----|------|------------
{{range $err := .ErrorCodes}}| `{{$err}}` | {{$err.Descriptor.Message}} | {{$err.Descriptor.Description|removenewlines}} |
{{end}}
{{end}}{{end}}{{end}}{{end}}{{end}}{{end}}
{{end}}

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# Docker Registry v2 authentication via central service
Today a Docker Registry can run in standalone mode in which there are no
authorization checks. While adding your own HTTP authorization requirements in
a proxy placed between the client and the registry can give you greater access
control, we'd like a native authorization mechanism that's public key based
with access control lists managed separately with the ability to have fine
granularity in access control on a by-key, by-user, by-namespace, and
by-repository basis. In v1 this can be configured by specifying an
`index_endpoint` in the registry's config. Clients present tokens generated by
the index and tokens are validated on-line by the registry with every request.
This results in a complex authentication and authorization loop that occurs
with every registry operation. Some people are very familiar with this image:
![index auth](https://docs.docker.com/static_files/docker_pull_chart.png)
The above image outlines the 6-step process in accessing the Official Docker
Registry.
1. Contact the Docker Hub to know where I should download “samalba/busybox”
2. Docker Hub replies:
a. samalba/busybox is on Registry A
b. here are the checksums for samalba/busybox (for all layers)
c. token
3. Contact Registry A to receive the layers for samalba/busybox (all of them to
the base image). Registry A is authoritative for “samalba/busybox” but keeps
a copy of all inherited layers and serve them all from the same location.
4. Registry contacts Docker Hub to verify if token/user is allowed to download
images.
5. Docker Hub returns true/false lettings registry know if it should proceed or
error out.
6. Get the payload for all layers.
The goal of this document is to outline a way to eliminate steps 4 and 5 from
the above process by using cryptographically signed tokens and no longer
require the client to authenticate each request with a username and password
stored locally in plain text.
The new registry workflow is more like this:
![v2 registry auth](https://docs.google.com/drawings/d/1EHZU9uBLmcH0kytDClBv6jv6WR4xZjE8RKEUw1mARJA/pub?w=480&h=360)
1. Attempt to begin a push/pull operation with the registry.
2. If the registry requires authorization it will return a `401 Unauthorized`
HTTP response with information on how to authenticate.
3. The registry client makes a request to the authorization service for a
signed JSON Web Token.
4. The authorization service returns a token.
5. The client retries the original request with the token embedded in the
request header.
6. The Registry authorizes the client and begins the push/pull session as
usual.
## Requirements
- Registry Clients capable of generating key pairs which can be used to
authenticate to an authorization server.
- An authorization server capable of managing user accounts, their public keys,
and access controls to their resources hosted by any given service (such as
repositories in a Docker Registry).
- A Docker Registry capable of trusting the authorization server to sign tokens
which clients can use for authorization and the ability to verify these
tokens for single use or for use during a sufficiently short period of time.
## Authorization Server Endpoint Descriptions
This document borrows heavily from the [JSON Web Token Draft Spec](https://tools.ietf.org/html/draft-ietf-oauth-json-web-token-32)
The described server is meant to serve as a user account and key manager and a
centralized access control list for resources hosted by other services which
wish to authenticate and manage authorizations using this services accounts and
their public keys.
Such a service could be used by the official docker registry to authenticate
clients and verify their authorization to docker image repositories.
Docker will need to be updated to interact with an authorization server to get
an authorization token.
## How to authenticate
Today, registry clients first contact the index to initiate a push or pull.
For v2, clients should contact the registry first. If the registry server
requires authentication it will return a `401 Unauthorized` response with a
`WWW-Authenticate` header detailing how to authenticate to this registry.
For example, say I (username `jlhawn`) am attempting to push an image to the
repository `samalba/my-app`. For the registry to authorize this, I either need
`push` access to the `samalba/my-app` repository or `push` access to the whole
`samalba` namespace in general. The registry will first return this response:
```
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="https://auth.docker.com/v2/token/",service="registry.docker.com",scope="repository:samalba/my-app:push"
```
This format is documented in [Section 3 of RFC 6750: The OAuth 2.0 Authorization Framework: Bearer Token Usage](https://tools.ietf.org/html/rfc6750#section-3)
The client will then know to make a `GET` request to the URL
`https://auth.docker.com/v2/token/` using the `service` and `scope` values from
the `WWW-Authenticate` header.
## Requesting a Token
#### Query Parameters
<dl>
<dt>
<code>service</code>
</dt>
<dd>
The name of the service which hosts the resource.
</dd>
<dt>
<code>scope</code>
</dt>
<dd>
The resource in question, formatted as one of the space-delimited
entries from the <code>scope</code> parameters from the <code>WWW-Authenticate</code> header
shown above. This query parameter should be specified multiple times if
there is more than one <code>scope</code> entry from the <code>WWW-Authenticate</code>
header. The above example would be specified as:
<code>scope=repository:samalba/my-app:push</code>.
</dd>
<dt>
<code>account</code>
</dt>
<dd>
The name of the account which the client is acting as. Optional if it
can be inferred from client authentication.
</dd>
</dl>
#### Description
Requests an authorization token for access to a specific resource hosted by a
specific service provider. Requires the client to authenticate either using a
TLS client certificate or using basic authentication (or any other kind of
digest/challenge/response authentication scheme if the client doesn't support
TLS client certs). If the key in the client certificate is linked to an account
then the token is issued for that account key. If the key in the certificate is
linked to multiple accounts then the client must specify the `account` query
parameter. The returned token is in JWT (JSON Web Token) format, signed using
the authorization server's private key.
#### Example
For this example, the client makes an HTTP request to the following endpoint
over TLS using a client certificate with the server being configured to allow a
non-verified issuer during the handshake (i.e., a self-signed client cert is
okay).
```
GET /v2/token/?service=registry.docker.com&scope=repository:samalba/my-app:push&account=jlhawn HTTP/1.1
Host: auth.docker.com
```
The server first inspects the client certificate to extract the subject key and
lookup which account it is associated with. The client is now authenticated
using that account.
The server next searches its access control list for the account's access to
the repository `samalba/my-app` hosted by the service `registry.docker.com`.
The server will now construct a JSON Web Token to sign and return. A JSON Web
Token has 3 main parts:
1. Headers
The header of a JSON Web Token is a standard JOSE header. The "typ" field
will be "JWT" and it will also contain the "alg" which identifies the
signing algorithm used to produce the signature. It will also usually have
a "kid" field, the ID of the key which was used to sign the token.
Here is an example JOSE Header for a JSON Web Token (formatted with
whitespace for readability):
```
{
"typ": "JWT",
"alg": "ES256",
"kid": "PYYO:TEWU:V7JH:26JV:AQTZ:LJC3:SXVJ:XGHA:34F2:2LAQ:ZRMK:Z7Q6"
}
```
It specifies that this object is going to be a JSON Web token signed using
the key with the given ID using the Elliptic Curve signature algorithm
using a SHA256 hash.
2. Claim Set
The Claim Set is a JSON struct containing these standard registered claim
name fields:
<dl>
<dt>
<code>iss</code> (Issuer)
</dt>
<dd>
The issuer of the token, typically the fqdn of the authorization
server.
</dd>
<dt>
<code>sub</code> (Subject)
</dt>
<dd>
The subject of the token; the id of the client which requested it.
</dd>
<dt>
<code>aud</code> (Audience)
</dt>
<dd>
The intended audience of the token; the id of the service which
will verify the token to authorize the client/subject.
</dd>
<dt>
<code>exp</code> (Expiration)
</dt>
<dd>
The token should only be considered valid up to this specified date
and time.
</dd>
<dt>
<code>nbf</code> (Not Before)
</dt>
<dd>
The token should not be considered valid before this specified date
and time.
</dd>
<dt>
<code>iat</code> (Issued At)
</dt>
<dd>
Specifies the date and time which the Authorization server
generated this token.
</dd>
<dt>
<code>jti</code> (JWT ID)
</dt>
<dd>
A unique identifier for this token. Can be used by the intended
audience to prevent replays of the token.
</dd>
</dl>
The Claim Set will also contain a private claim name unique to this
authorization server specification:
<dl>
<dt>
<code>access</code>
</dt>
<dd>
An array of access entry objects with the following fields:
<dl>
<dt>
<code>type</code>
</dt>
<dd>
The type of resource hosted by the service.
</dd>
<dt>
<code>name</code>
</dt>
<dd>
The name of the recource of the given type hosted by the
service.
</dd>
<dt>
<code>actions</code>
</dt>
<dd>
An array of strings which give the actions authorized on
this resource.
</dd>
</dl>
</dd>
</dl>
Here is an example of such a JWT Claim Set (formatted with whitespace for
readability):
```
{
"iss": "auth.docker.com",
"sub": "jlhawn",
"aud": "registry.docker.com",
"exp": 1415387315,
"nbf": 1415387015,
"iat": 1415387015,
"jti": "tYJCO1c6cnyy7kAn0c7rKPgbV1H1bFws",
"access": [
{
"type": "repository",
"name": "samalba/my-app",
"actions": [
"push"
]
}
]
}
```
3. Signature
The authorization server will produce a JOSE header and Claim Set with no
extraneous whitespace, i.e., the JOSE Header from above would be
```
{"typ":"JWT","alg":"ES256","kid":"PYYO:TEWU:V7JH:26JV:AQTZ:LJC3:SXVJ:XGHA:34F2:2LAQ:ZRMK:Z7Q6"}
```
and the Claim Set from above would be
```
{"iss":"auth.docker.com","sub":"jlhawn","aud":"registry.docker.com","exp":1415387315,"nbf":1415387015,"iat":1415387015,"jti":"tYJCO1c6cnyy7kAn0c7rKPgbV1H1bFws","access":[{"type":"repository","name":"samalba/my-app","actions":["push"]}]}
```
The utf-8 representation of this JOSE header and Claim Set are then
url-safe base64 encoded (sans trailing '=' buffer), producing:
```
eyJ0eXAiOiJKV1QiLCJhbGciOiJFUzI1NiIsImtpZCI6IlBZWU86VEVXVTpWN0pIOjI2SlY6QVFUWjpMSkMzOlNYVko6WEdIQTozNEYyOjJMQVE6WlJNSzpaN1E2In0
```
for the JOSE Header and
```
eyJpc3MiOiJhdXRoLmRvY2tlci5jb20iLCJzdWIiOiJqbGhhd24iLCJhdWQiOiJyZWdpc3RyeS5kb2NrZXIuY29tIiwiZXhwIjoxNDE1Mzg3MzE1LCJuYmYiOjE0MTUzODcwMTUsImlhdCI6MTQxNTM4NzAxNSwianRpIjoidFlKQ08xYzZjbnl5N2tBbjBjN3JLUGdiVjFIMWJGd3MiLCJhY2Nlc3MiOlt7InR5cGUiOiJyZXBvc2l0b3J5IiwibmFtZSI6InNhbWFsYmEvbXktYXBwIiwiYWN0aW9ucyI6WyJwdXNoIl19XX0
```
for the Claim Set. These two are concatenated using a '.' character,
yielding the string:
```
eyJ0eXAiOiJKV1QiLCJhbGciOiJFUzI1NiIsImtpZCI6IlBZWU86VEVXVTpWN0pIOjI2SlY6QVFUWjpMSkMzOlNYVko6WEdIQTozNEYyOjJMQVE6WlJNSzpaN1E2In0.eyJpc3MiOiJhdXRoLmRvY2tlci5jb20iLCJzdWIiOiJqbGhhd24iLCJhdWQiOiJyZWdpc3RyeS5kb2NrZXIuY29tIiwiZXhwIjoxNDE1Mzg3MzE1LCJuYmYiOjE0MTUzODcwMTUsImlhdCI6MTQxNTM4NzAxNSwianRpIjoidFlKQ08xYzZjbnl5N2tBbjBjN3JLUGdiVjFIMWJGd3MiLCJhY2Nlc3MiOlt7InR5cGUiOiJyZXBvc2l0b3J5IiwibmFtZSI6InNhbWFsYmEvbXktYXBwIiwiYWN0aW9ucyI6WyJwdXNoIl19XX0
```
This is then used as the payload to a the `ES256` signature algorithm
specified in the JOSE header and specified fully in [Section 3.4 of the JSON Web Algorithms (JWA)
draft specification](https://tools.ietf.org/html/draft-ietf-jose-json-web-algorithms-38#section-3.4)
This example signature will use the following ECDSA key for the server:
```
{
"kty": "EC",
"crv": "P-256",
"kid": "PYYO:TEWU:V7JH:26JV:AQTZ:LJC3:SXVJ:XGHA:34F2:2LAQ:ZRMK:Z7Q6",
"d": "R7OnbfMaD5J2jl7GeE8ESo7CnHSBm_1N2k9IXYFrKJA",
"x": "m7zUpx3b-zmVE5cymSs64POG9QcyEpJaYCD82-549_Q",
"y": "dU3biz8sZ_8GPB-odm8Wxz3lNDr1xcAQQPQaOcr1fmc"
}
```
A resulting signature of the above payload using this key is:
```
QhflHPfbd6eVF4lM9bwYpFZIV0PfikbyXuLx959ykRTBpe3CYnzs6YBK8FToVb5R47920PVLrh8zuLzdCr9t3w
```
Concatenating all of these together with a `.` character gives the
resulting JWT:
```
eyJ0eXAiOiJKV1QiLCJhbGciOiJFUzI1NiIsImtpZCI6IlBZWU86VEVXVTpWN0pIOjI2SlY6QVFUWjpMSkMzOlNYVko6WEdIQTozNEYyOjJMQVE6WlJNSzpaN1E2In0.eyJpc3MiOiJhdXRoLmRvY2tlci5jb20iLCJzdWIiOiJqbGhhd24iLCJhdWQiOiJyZWdpc3RyeS5kb2NrZXIuY29tIiwiZXhwIjoxNDE1Mzg3MzE1LCJuYmYiOjE0MTUzODcwMTUsImlhdCI6MTQxNTM4NzAxNSwianRpIjoidFlKQ08xYzZjbnl5N2tBbjBjN3JLUGdiVjFIMWJGd3MiLCJhY2Nlc3MiOlt7InR5cGUiOiJyZXBvc2l0b3J5IiwibmFtZSI6InNhbWFsYmEvbXktYXBwIiwiYWN0aW9ucyI6WyJwdXNoIl19XX0.QhflHPfbd6eVF4lM9bwYpFZIV0PfikbyXuLx959ykRTBpe3CYnzs6YBK8FToVb5R47920PVLrh8zuLzdCr9t3w
```
This can now be placed in an HTTP response and returned to the client to use to
authenticate to the audience service:
```
HTTP/1.1 200 OK
Content-Type: application/json
{"token": "eyJ0eXAiOiJKV1QiLCJhbGciOiJFUzI1NiIsImtpZCI6IlBZWU86VEVXVTpWN0pIOjI2SlY6QVFUWjpMSkMzOlNYVko6WEdIQTozNEYyOjJMQVE6WlJNSzpaN1E2In0.eyJpc3MiOiJhdXRoLmRvY2tlci5jb20iLCJzdWIiOiJqbGhhd24iLCJhdWQiOiJyZWdpc3RyeS5kb2NrZXIuY29tIiwiZXhwIjoxNDE1Mzg3MzE1LCJuYmYiOjE0MTUzODcwMTUsImlhdCI6MTQxNTM4NzAxNSwianRpIjoidFlKQ08xYzZjbnl5N2tBbjBjN3JLUGdiVjFIMWJGd3MiLCJhY2Nlc3MiOlt7InR5cGUiOiJyZXBvc2l0b3J5IiwibmFtZSI6InNhbWFsYmEvbXktYXBwIiwiYWN0aW9ucyI6WyJwdXNoIl19XX0.QhflHPfbd6eVF4lM9bwYpFZIV0PfikbyXuLx959ykRTBpe3CYnzs6YBK8FToVb5R47920PVLrh8zuLzdCr9t3w"}
```
## Using the signed token
Once the client has a token, it will try the registry request again with the
token placed in the HTTP `Authorization` header like so:
```
Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJFUzI1NiIsImtpZCI6IkJWM0Q6MkFWWjpVQjVaOktJQVA6SU5QTDo1RU42Ok40SjQ6Nk1XTzpEUktFOkJWUUs6M0ZKTDpQT1RMIn0.eyJpc3MiOiJhdXRoLmRvY2tlci5jb20iLCJzdWIiOiJCQ0NZOk9VNlo6UUVKNTpXTjJDOjJBVkM6WTdZRDpBM0xZOjQ1VVc6NE9HRDpLQUxMOkNOSjU6NUlVTCIsImF1ZCI6InJlZ2lzdHJ5LmRvY2tlci5jb20iLCJleHAiOjE0MTUzODczMTUsIm5iZiI6MTQxNTM4NzAxNSwiaWF0IjoxNDE1Mzg3MDE1LCJqdGkiOiJ0WUpDTzFjNmNueXk3a0FuMGM3cktQZ2JWMUgxYkZ3cyIsInNjb3BlIjoiamxoYXduOnJlcG9zaXRvcnk6c2FtYWxiYS9teS1hcHA6cHVzaCxwdWxsIGpsaGF3bjpuYW1lc3BhY2U6c2FtYWxiYTpwdWxsIn0.Y3zZSwaZPqy4y9oRBVRImZyv3m_S9XDHF1tWwN7mL52C_IiA73SJkWVNsvNqpJIn5h7A2F8biv_S2ppQ1lgkbw
```
This is also described in [Section 2.1 of RFC 6750: The OAuth 2.0 Authorization Framework: Bearer Token Usage](https://tools.ietf.org/html/rfc6750#section-2.1)
## Verifying the token
The registry must now verify the token presented by the user by inspecting the
claim set within. The registry will:
- Ensure that the issuer (`iss` claim) is an authority it trusts.
- Ensure that the registry identifies as the audience (`aud` claim).
- Check that the current time is between the `nbf` and `exp` claim times.
- If enforcing single-use tokens, check that the JWT ID (`jti` claim) value has
not been seen before.
- To enforce this, the registry may keep a record of `jti`s it has seen for
up to the `exp` time of the token to prevent token replays.
- Check the `access` claim value and use the identified resources and the list
of actions authorized to determine whether the token grants the required
level of access for the operation the client is attempting to perform.
- Verify that the signature of the token is valid.
At no point in this process should the registry need to <em>call back</em> to
the authorization server. If anything, it would only need to update a list of
trusted public keys for verifying token signatures or use a separate API
(still to be spec'd) to add/update resource records on the authorization
server.

77
docs/spec/json.md Normal file
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@ -0,0 +1,77 @@
# Docker Distribution JSON Canonicalization
## Introduction
To provide consistent content hashing of JSON objects throughout Docker
Distribution APIs, a canonical JSON format has been defined. Adopting such a
canonicalization also aids in caching JSON responses.
## Rules
Compliant JSON should conform to the following rules:
1. All generated JSON should comply with [RFC
7159](http://www.ietf.org/rfc/rfc7159.txt).
2. Resulting "JSON text" shall always be encoded in UTF-8.
3. Unless a canonical key order is defined for a particular schema, object
keys shall always appear in lexically sorted order.
4. All whitespace between tokens should be removed.
5. No "trailing commas" are allowed in object or array definitions.
## Examples
The following is a simple example of a canonicalized JSON string:
```json
{"asdf":1,"qwer":[],"zxcv":[{},true,1000000000,"tyui"]}
```
## Reference
### Other Canonicalizations
The OLPC project specifies [Canonical
JSON](http://wiki.laptop.org/go/Canonical_JSON). While this is used in
[TUF](http://theupdateframework.com/), which may be used with other
distribution-related protocols, this alternative format has been proposed in
case the original source changes. Specifications complying with either this
specification or an alternative should explicitly call out the
canonicalization format. Except for key ordering, this specification is mostly
compatible.
### Go
In Go, the [`encoding/json`](http://golang.org/pkg/encoding/json/) library
will emit canonical JSON by default. Simply using `json.Marshal` will suffice
in most cases:
```go
incoming := map[string]interface{}{
"asdf": 1,
"qwer": []interface{}{},
"zxcv": []interface{}{
map[string]interface{}{},
true,
int(1e9),
"tyui",
},
}
canonical, err := json.Marshal(incoming)
if err != nil {
// ... handle error
}
```
To apply canonical JSON format spacing to an existing serialized JSON buffer, one
can use
[`json.Indent`](http://golang.org/src/encoding/json/indent.go?s=1918:1989#L65)
with the following arguments:
```go
incoming := getBytes()
var canonical bytes.Buffer
if err := json.Indent(&canonical, incoming, "", ""); err != nil {
// ... handle error
}
```