Integrate auth.AccessController into registry app

This changeset integrates the AccessController into the main registry app. This
includes support for configuration and a test implementation, called "silly"
auth. Auth is only enabled if the configuration is present but takes measure to
ensure that configuration errors don't allow the appserver to start with open
access.

configuration/configuration.go

@@ -20,6 +20,10 @@ type Configuration struct {
 	// Storage is the configuration for the registry's storage driver
 	Storage Storage `yaml:"storage"`
 
+	// Auth allows configuration of various authorization methods that may be
+	// used to gate requests.
+	Auth Auth `yaml:"auth"`
+
 	// Reporting is the configuration for error reporting
 	Reporting Reporting `yaml:"reporting"`
 
@@ -85,6 +89,9 @@ func (loglevel *Loglevel) UnmarshalYAML(unmarshal func(interface{}) error) error
 	return nil
 }
 
+// Parameters defines a key-value parameters mapping
+type Parameters map[string]interface{}
+
 // Storage defines the configuration for registry object storage
 type Storage map[string]Parameters
 
@@ -137,13 +144,71 @@ func (storage *Storage) UnmarshalYAML(unmarshal func(interface{}) error) error {
 // MarshalYAML implements the yaml.Marshaler interface
 func (storage Storage) MarshalYAML() (interface{}, error) {
 	if storage.Parameters() == nil {
-		return storage.Type, nil
+		return storage.Type(), nil
 	}
 	return map[string]Parameters(storage), nil
 }
 
-// Parameters defines a key-value parameters mapping
-type Parameters map[string]interface{}
+// Auth defines the configuration for registry authorization.
+type Auth map[string]Parameters
+
+// Type returns the storage driver type, such as filesystem or s3
+func (auth Auth) Type() string {
+	// Return only key in this map
+	for k := range auth {
+		return k
+	}
+	return ""
+}
+
+// Parameters returns the Parameters map for an Auth configuration
+func (auth Auth) Parameters() Parameters {
+	return auth[auth.Type()]
+}
+
+// setParameter changes the parameter at the provided key to the new value
+func (auth Auth) setParameter(key string, value interface{}) {
+	auth[auth.Type()][key] = value
+}
+
+// UnmarshalYAML implements the yaml.Unmarshaler interface
+// Unmarshals a single item map into a Storage or a string into a Storage type with no parameters
+func (auth *Auth) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var m map[string]Parameters
+	err := unmarshal(&m)
+	if err == nil {
+		if len(m) > 1 {
+			types := make([]string, 0, len(m))
+			for k := range m {
+				types = append(types, k)
+			}
+
+			// TODO(stevvooe): May want to change this slightly for
+			// authorization to allow multiple challenges.
+			return fmt.Errorf("must provide exactly one type. Provided: %v", types)
+
+		}
+		*auth = m
+		return nil
+	}
+
+	var authType string
+	err = unmarshal(&authType)
+	if err == nil {
+		*auth = Auth{authType: Parameters{}}
+		return nil
+	}
+
+	return err
+}
+
+// MarshalYAML implements the yaml.Marshaler interface
+func (auth Auth) MarshalYAML() (interface{}, error) {
+	if auth.Parameters() == nil {
+		return auth.Type(), nil
+	}
+	return map[string]Parameters(auth), nil
+}
 
 // Reporting defines error reporting methods.
 type Reporting struct {