Adds auth package with token auth backend

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

auth/token/util.go

@@ -0,0 +1,77 @@
+package token
+
+import (
+	"encoding/base64"
+	"errors"
+	"strings"
+)
+
+// joseBase64UrlEncode encodes the given data using the standard base64 url
+// encoding format but with all trailing '=' characters ommitted in accordance
+// with the jose specification.
+// http://tools.ietf.org/html/draft-ietf-jose-json-web-signature-31#section-2
+func joseBase64UrlEncode(b []byte) string {
+	return strings.TrimRight(base64.URLEncoding.EncodeToString(b), "=")
+}
+
+// joseBase64UrlDecode decodes the given string using the standard base64 url
+// decoder but first adds the appropriate number of trailing '=' characters in
+// accordance with the jose specification.
+// http://tools.ietf.org/html/draft-ietf-jose-json-web-signature-31#section-2
+func joseBase64UrlDecode(s string) ([]byte, error) {
+	switch len(s) % 4 {
+	case 0:
+	case 2:
+		s += "=="
+	case 3:
+		s += "="
+	default:
+		return nil, errors.New("illegal base64url string")
+	}
+	return base64.URLEncoding.DecodeString(s)
+}
+
+// stringSet is a useful type for looking up strings.
+type stringSet map[string]struct{}
+
+func newStringSet(strs ...string) stringSet {
+	set := make(stringSet, len(strs))
+	for _, str := range strs {
+		set[str] = struct{}{}
+	}
+
+	return set
+}
+
+// contains returns whether the given key is in this StringSet.
+func (ss stringSet) contains(key string) bool {
+	_, ok := ss[key]
+	return ok
+}
+
+// keys returns a slice of all keys in this stringSet.
+func (ss stringSet) keys() []string {
+	keys := make([]string, 0, len(ss))
+
+	for key := range ss {
+		keys = append(keys, key)
+	}
+
+	return keys
+}
+
+// actionSet is a special type of stringSet.
+type actionSet stringSet
+
+// contains calls stringSet.contains() for
+// either "*" or the given action string.
+func (s actionSet) contains(action string) bool {
+	ss := stringSet(s)
+
+	return ss.contains("*") || ss.contains(action)
+}
+
+// keys wraps stringSet.keys()
+func (s actionSet) keys() []string {
+	return stringSet(s).keys()
+}