[docs/spec/auth] Clarify the Token auth workflow
Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)pull/973/head
Josh Hawn
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@ -46,7 +46,7 @@ the above process by using cryptographically signed tokens and no longer
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require the client to authenticate each request with a username and password
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stored locally in plain text.
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The new registry workflow is more like this:
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The v2 registry token workflow is more like this:
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@ -55,19 +55,20 @@ The new registry workflow is more like this:
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HTTP response with information on how to authenticate.
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3. The registry client makes a request to the authorization service for a
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signed JSON Web Token.
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4. The authorization service returns a token.
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4. The authorization service returns an opaque token representing the client's
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authorized access.
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5. The client retries the original request with the token embedded in the
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request header.
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6. The Registry authorizes the client and begins the push/pull session as
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usual.
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6. The Registry authorizes the client by validating the token and the claim set
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embedded within it and begins the push/pull session as usual.
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## Requirements
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- Registry Clients capable of generating key pairs which can be used to
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authenticate to an authorization server.
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- An authorization server capable of managing user accounts, their public keys,
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and access controls to their resources hosted by any given service (such as
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repositories in a Docker Registry).
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- Registry clients which can understand and respond to token auth challenges
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returned by the resource server.
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- An authorization server capable of managing access controls to their
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resources hosted by any given service (such as repositories in a Docker
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Registry).
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- A Docker Registry capable of trusting the authorization server to sign tokens
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which clients can use for authorization and the ability to verify these
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tokens for single use or for use during a sufficiently short period of time.
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@ -76,39 +77,55 @@ The new registry workflow is more like this:
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This document borrows heavily from the [JSON Web Token Draft Spec](https://tools.ietf.org/html/draft-ietf-oauth-json-web-token-32)
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The described server is meant to serve as a user account and key manager and a
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centralized access control list for resources hosted by other services which
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wish to authenticate and manage authorizations using this services accounts and
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their public keys.
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The described server is meant to serve as a standalone access control manager
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for resources hosted by other services which wish to authenticate and manage
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authorizations using a separate access control manager.
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Such a service could be used by the official docker registry to authenticate
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clients and verify their authorization to docker image repositories.
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Such a service could be used by the official Docker Registry to authenticate
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clients and verify their authorization to Docker image repositories.
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Docker will need to be updated to interact with an authorization server to get
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an authorization token.
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As of Docker 1.6, the registry client within the Docker Engine has been updated
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to handle such an authorization workflow.
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## How to authenticate
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Today, registry clients first contact the index to initiate a push or pull.
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For v2, clients should contact the registry first. If the registry server
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requires authentication it will return a `401 Unauthorized` response with a
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`WWW-Authenticate` header detailing how to authenticate to this registry.
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Registry V1 clients first contact the index to initiate a push or pull. Under
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the Registry V2 workflow, clients should contact the registry first. If the
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registry server requires authentication it will return a `401 Unauthorized`
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response with a `WWW-Authenticate` header detailing how to authenticate to this
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registry.
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For example, say I (username `jlhawn`) am attempting to push an image to the
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repository `samalba/my-app`. For the registry to authorize this, I either need
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`push` access to the `samalba/my-app` repository or `push` access to the whole
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`samalba` namespace in general. The registry will first return this response:
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repository `samalba/my-app`. For the registry to authorize this, I will need
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`push` access to the `samalba/my-app` repository. The registry will first
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return this response:
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```
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HTTP/1.1 401 Unauthorized
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WWW-Authenticate: Bearer realm="https://auth.docker.com/v2/token/",service="registry.docker.com",scope="repository:samalba/my-app:push"
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Content-Type: application/json; charset=utf-8
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Docker-Distribution-Api-Version: registry/2.0
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Www-Authenticate: Bearer realm="https://auth.docker.io/token",service="registry.docker.io",scope="repository:samalba/my-app:pull,push"
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Date: Thu, 10 Sep 2015 19:32:31 GMT
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Content-Length: 235
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Strict-Transport-Security: max-age=31536000
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{"errors":[{"code":"UNAUTHORIZED","message":"access to the requested resource is not authorized","detail":[{"Type":"repository","Name":"samalba/my-app","Action":"pull"},{"Type":"repository","Name":"samalba/my-app","Action":"push"}]}]}
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```
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Note the HTTP Response Header indicating the auth challenge:
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```
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Www-Authenticate: Bearer realm="https://auth.docker.io/token",service="registry.docker.io",scope="repository:samalba/my-app:pull,push"
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```
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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)
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The client will then know to make a `GET` request to the URL
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`https://auth.docker.com/v2/token/` using the `service` and `scope` values from
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the `WWW-Authenticate` header.
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This challenge indicates that the registry requires a token issued by the
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specified token server and that the request the client is attempting will
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need to include sufficient access entries in its claim set. To respond to this
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challenge, the client will need to make a `GET` request to the URL
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`https://auth.docker.io/token` using the `service` and `scope` values from the
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`WWW-Authenticate` header.
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## Requesting a Token
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@ -132,45 +149,51 @@ the `WWW-Authenticate` header.
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header. The above example would be specified as:
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<code>scope=repository:samalba/my-app:push</code>.
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</dd>
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<dt>
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<code>account</code>
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</dt>
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<dd>
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The name of the account which the client is acting as. Optional if it
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can be inferred from client authentication.
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</dd>
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</dl>
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#### Description
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#### Example Token Request
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Requests an authorization token for access to a specific resource hosted by a
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specific service provider. Requires the client to authenticate either using a
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TLS client certificate or using basic authentication (or any other kind of
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digest/challenge/response authentication scheme if the client doesn't support
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TLS client certs). If the key in the client certificate is linked to an account
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then the token is issued for that account key. If the key in the certificate is
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linked to multiple accounts then the client must specify the `account` query
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parameter. The returned token is in JWT (JSON Web Token) format, signed using
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the authorization server's private key.
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#### Example
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For this example, the client makes an HTTP request to the following endpoint
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over TLS using a client certificate with the server being configured to allow a
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non-verified issuer during the handshake (i.e., a self-signed client cert is
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okay).
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For this example, the client makes an HTTP GET request to the following URL:
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```
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GET /v2/token/?service=registry.docker.com&scope=repository:samalba/my-app:push&account=jlhawn HTTP/1.1
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Host: auth.docker.com
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https://auth.docker.io/token?service=registry.docker.io&scope=repository:samalba/my-app:pull,push
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```
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The server first inspects the client certificate to extract the subject key and
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lookup which account it is associated with. The client is now authenticated
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using that account.
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The token server should first attempt to authenticate the client using any
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authentication credentials provided with the request. As of Docker 1.8, the
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registry client in the Docker Engine only supports Basic Authentication to
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these token servers. If an attempt to authenticate to the token server fails,
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the token server should return a `401 Unauthorized` response indicating that
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the provided credentials are invalid.
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The server next searches its access control list for the account's access to
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the repository `samalba/my-app` hosted by the service `registry.docker.com`.
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Whether the token server requires authentication is up to the policy of that
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access control provider. Some requests may require authentication to determine
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access (such as pushing or pulling a private repository) while others may not
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(such as pulling from a public repository).
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After authenticating the client (which may simply be an anonymous client if
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no attempt was made to authenticate), the token server must next query its
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access control list to determine whether the client has the requested scope. In
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this example request, if I have authenticated as user `jlhawn`, the token
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server will determine what access I have to the repository `samalba/my-app`
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hosted by the entity `registry.docker.io`.
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Once the token server has determined what access the client has to the
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resources requested in the `scope` parameter, it will take the intersection of
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the set of requested actions on each resource and the set of actions that the
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client has in fact been granted. If the client only has a subset of the
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requested access **it must not be considered an error** as it is not the
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responsibility of the token server to indicate authorization errors as part of
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this workflow.
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Continuing with the example request, the token server will find that the
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client's set of granted access to the repository is `[pull, push]` which when
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intersected with the requested access `[pull, push]` yields an equal set. If
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the granted access set was found only to be `[pull]` then the intersected set
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would only be `[pull]`. If the client has no access to the repository then the
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intersected set would be empty, `[]`.
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It is this intersected set of access which is placed in the returned token.
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The server will now construct a JSON Web Token to sign and return. A JSON Web
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Token has 3 main parts:
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@ -214,14 +237,16 @@ Token has 3 main parts:
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<code>sub</code> (Subject)
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</dt>
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<dd>
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The subject of the token; the id of the client which requested it.
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The subject of the token; the name or id of the client which
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requested it. This should be empty (`""`) if the client did not
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authenticate.
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</dd>
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<dt>
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<code>aud</code> (Audience)
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</dt>
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<dd>
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The intended audience of the token; the id of the service which
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will verify the token to authorize the client/subject.
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The intended audience of the token; the name or id of the service
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which will verify the token to authorize the client/subject.
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</dd>
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<dt>
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<code>exp</code> (Expiration)
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@ -305,6 +330,7 @@ Token has 3 main parts:
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"type": "repository",
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"name": "samalba/my-app",
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"actions": [
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"pull",
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"push"
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]
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}
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@ -416,8 +442,16 @@ claim set within. The registry will:
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level of access for the operation the client is attempting to perform.
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- Verify that the signature of the token is valid.
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At no point in this process should the registry need to <em>call back</em> to
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the authorization server. If anything, it would only need to update a list of
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trusted public keys for verifying token signatures or use a separate API
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(still to be spec'd) to add/update resource records on the authorization
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server.
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If any of these requirements are not met, the registry will return a
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`403 Forbidden` response to indicate that the token is invalid.
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**Note**: it is only at this point in the workflow that an authorization error
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may occur. The token server should *not* return errors when the user does not
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have the requested authorization. Instead, the returned token should indicate
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whatever of the requested scope the client does have (the intersection of
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requested and granted access). If the token does not supply proper
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authorization then the registry will return the appropriate error.
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At no point in this process should the registry need to call back to the
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authorization server. The registry only needs to be supplied with the trusted
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public keys to verify the token signatures.
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