[api spec] Update authN and authZ errors

Associate HTTP 401s with Authentication errors rather than Authorization
errors. Changes the meaning of the UNAUTHORIZED error to be authentication
specific.

Defines DENIED error code to be associated with authorization
errors which result in HTTP 403 responses.

Add 'No Such Repository' errors to more endpoints.

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

docs/api/errcode/register.go

@@ -33,16 +33,28 @@ var (
 		HTTPStatusCode: http.StatusMethodNotAllowed,
 	})
 
-	// ErrorCodeUnauthorized is returned if a request is not authorized.
+	// ErrorCodeUnauthorized is returned if a request requires
+	// authentication.
 	ErrorCodeUnauthorized = Register("errcode", ErrorDescriptor{
 		Value:   "UNAUTHORIZED",
-		Message: "access to the requested resource is not authorized",
-		Description: `The access controller denied access for the operation on
-		a resource. Often this will be accompanied by a 401 Unauthorized
-		response status.`,
+		Message: "authentication required",
+		Description: `The access controller was unable to authenticate
+		the client. Often this will be accompanied by a
+		Www-Authenticate HTTP response header indicating how to
+		authenticate.`,
 		HTTPStatusCode: http.StatusUnauthorized,
 	})
 
+	// ErrorCodeDenied is returned if a client does not have sufficient
+	// permission to perform an action.
+	ErrorCodeDenied = Register("errcode", ErrorDescriptor{
+		Value:   "DENIED",
+		Message: "requested access to the resource is denied",
+		Description: `The access controller denied access for the
+		operation on a resource.`,
+		HTTPStatusCode: http.StatusForbidden,
+	})
+
 	// ErrorCodeUnavailable provides a common error to report unavialability
 	// of a service or endpoint.
 	ErrorCodeUnavailable = Register("errcode", ErrorDescriptor{