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Issue Access Tokens with AuthController

An application using Aqueduct's Auth framework must have endpoints to exchange credentials for access tokens. While a developer could implement these endpoints themselves and talk directly to an AuthServer, the OAuth 2.0 specification is where happiness goes to die. Therefore, there exist two RequestControllers in Aqueduct that handle granting and refreshing authorization tokens - AuthController and AuthCodeController.

Issue, Refresh and Exchange Tokens with AuthController

An AuthController grants access tokens and refreshes them. It also exchanges authorization codes obtained from AuthCodeController for access tokens.

Using an AuthController in an application is straightforward - hook it up to a Router and pass it an AuthServer.

@override
void setupRouter(Router router) {
  router
    .route("/auth/token")
    .generate(() => new AuthController(authServer));
}

To grant an access token, a client application sends a HTTP POST to the controller. The request must have:

  • an Authorization header with the Client ID and Client Secret (if one exists) and,
  • a x-www-form-urlencoded body with the username and password of the authenticating user.

The body must also contain the key-value pair grant_type=password. For example, the following Dart code will initiate successful authentication:

var clientID = "com.app.demo";
var clientSecret = "mySecret";
var body = "[email protected]&password=foobar&grant_type=password";
var clientCredentials = new Base64Encoder().convert("$clientID:$clientSecret".codeUnits);

var response = await http.post(
  "https://stablekernel.com/auth/token",
  headers: {
    "Content-Type": "application/x-www-form-urlencoded",
    "Authorization": "Basic $clientCredentials"
  },
  body: body);

If the OAuth 2.0 client ID is public - that is, it does not have a client secret - the secret is omitted from the authorization header:

// Notice that the separating colon (:) is still present.
var clientCredentials = new Base64Encoder().convert("$clientID:".codeUnits);

The response to a password token request is a JSON body that follows the OAuth 2.0 specification:

{
  "access_token": "..."
  "refresh_token": "...",
  "expires_in": 3600,
  "token_type": "bearer"
}

Tokens are refreshed through the same endpoint, but with a payload that only contains the refresh token and grant_type=refresh_token.

grant_type=refresh_token&refresh_token=kjasdiuz9u3namnsd

See Aqueduct Auth CLI for more details on creating OAuth 2.0 client identifier and secrets.

If an Aqueduct application is using scope, an additional scope parameter can contain a space-delimited list of requested authorization scope. Only allowed scopes are returned and granted, and if no scopes are allowed then the request fails. If scope is provided, granted scope will be available in the response body.

It is important that an Authorizer must not protect instances of AuthController. The Authorization header is parsed and verified by AuthController.

Once granted, an access token can be used to pass Authorizer.bearer()s in the request controller channel.

Issue Authorization Codes with AuthCodeController

An AuthCodeController manages the OAuth 2.0 authorization code flow. The authorization code flow is used when an Aqueduct application allows third party applications access to authorized resources.

Let's say you've built an Aqueduct application that allows people to store notes for themselves. Now, a friend approaches you with their application that is a to-do list. Instead of building their own note-taking feature, your friend wants users of their application to access the notes the user has stored in your application. While trustworthy, you don't want your friend to have access to the username and passwords of your subscribers.

Your friend adds a link to their application that takes the user to an HTML page hosted by your server. The user enters their credentials in this page, which sends a POST request to your server. Your server responds by redirecting the user's browser back into your friend's application. An authorization code is included in the query string of the redirect URL.

Your friend's application parses the code from the URL and sends it to their server. Behind the scenes, their server exchanges this code with your server for an access token.

An AuthCodeController responds to both GET and POST requests. When issued a GET, it serves up a HTML page with a login form. This login form's submit action sends a POST to the same endpoint with the username and password of the user. Upon success, the response from the POST is a 302 redirect with an authorization code.

Setting up an AuthCodeController is nearly as simple as setting up an AuthController, but requires a function that renders the HTML login form. Here's an example:

@override
void setupRouter(Router router) {
  router
    .route("/auth/code")
    .generate(() => new AuthCodeController(
      authServer, renderAuthorizationPageHTML: renderLogin));
}

Future<String> renderLogin(
    AuthCodeController requestingController,
    URI requestURI,
    Map<String, String> queryParameters) {
  var html = HTMLRenderer.templateWithSubstitutions(
    "web/login.html", requestURI, queryParameters);

  return html;
}

It is important that all values passed to HTML rendering function are sent in the form's query parameters - they contain necessary security components and scope information.

When your friend's application links to your login page - GET /auth/code - they must include three query parameters: state, client_id, response_type. They may optionally include scope.

https://stablekernel.com/auth/code?client_id=friend.app&response_type=code&state=87uijn3rkja

The value of client_id must be created specifically for your friend's application and stored in your database. (See more on generating client identifiers with aqueduct auth in Aqueduct Auth CLI.) The response_type must always be code. The state must be a value your friend's application creates - it is often some random value like a session cookie.

When a user of your friend's application goes through this process, they are redirected back into your friend's application. Both the generated authorization code and the value for state will be query parameters in the URL. That redirect URL will look like:

https://friends.app/code_callback?code=abcd672kk&state=87uijn3rkja

The redirect URL is pre-determined when generating the client identifier with aqueduct auth.

Your friend's application verifies that state matches the state they sent in GET /auth/code. They then send the code to their server. The server then exchanges this code with your server by issuing a POST to an AuthController - NOT the AuthCodeController - with the following application/x-www-form-urlencoded body:

grant_type=authorization_code&code=abcd672kk

An access token will be returned to the server which your friend then stores in their database. Whenever one of their users makes a request that requires accessing your application's data, they will execute requests with that access token.