OAuth 2 Endpoints for Restify

This package provides a very simple OAuth 2.0 endpoint for the [Restify][] framework. In particular, it implements
the [Client Credentials][cc] and [Resource Owner Password Credentials][ropc] flows only.

What You Get

If you provide Restify–OAuth2 with the appropriate hooks, it will:

* Set up a [token endpoint][], which returns [access token responses][token-endpoint-success] or
[correctly-formatted error responses][token-endpoint-error].
* For all other resources, when an access token is [sent via the Authorization header][send-token], it will validate
it:
* If the token fails validation, it will send [an appropriate 400 or 401 error response][token-usage-error], with a
[WWW-Authenticate][www-authenticate] header and a [Link][web-linking] [rel="oauth2-token"][oauth2-token-rel]
header pointing to the token endpoint.
* Otherwise, you can use your authenticateToken and grantScopes hooks to set properties on the request object for
your routes to check later.
* If no access token is sent, it ensures that req.username is set to null; furthermore, none of your hooks are
called, so you can be sure that no properties that they set are present.
* You can then check for these conditions whenever there is a resource you want to protect.
* If the user tries to access a protected resource, you can use Restify–OAuth2's res.sendUnauthenticated() to send
appropriate 401 errors with helpful WWW-Authenticate and Link headers, or its res.sendUnauthorized() to send
appropriate 403 errors with similar headers.

Use and Configuration

To use Restify–OAuth2, you'll need to pass it your server plus some options, including the hooks discussed below.
Restify–OAuth2 also depends on the built-in authorizationParser and bodyParser plugins, the latter with mapParams
set to false. So in short, it looks like this:

``js
var restify = require("restify");
var restifyOAuth2 = require("restify-oauth2");

var server = restify.createServer({ name: "My cool server", version: "1.0.0" });
server.use(restify.authorizationParser());
server.use(restify.bodyParser({ mapParams: false }));

restifyOAuth2.cc(server, options);
// or
restifyOAuth2.ropc(server, options);
`

Unfortunately, Restify–OAuth2 can't be a simple Restify plugin. It needs to install a route for the token
endpoint, whereas plugins simply run on every request and don't modify the server's routing table.

Options

The options you pass to Restify–OAuth2 depend heavily on which of the two flows you are choosing. There are some
options common to both flows, but the options.hooks hash will vary depending on the flow. Once you provide the
appropriate hooks, you get an OAuth 2 implementation for free.

$3

The idea behind this very simple OAuth 2 flow is that your API clients identify themselves with client IDs and secrets,
and if those values authenticate, you grant them an access token they can use for further requests. The advantage of
this over simply requiring basic access authentication headers on every request is that now you can set those tokens to
expire, or revoke them if they fall in to the wrong hands.

To install Restify–OAuth2's client credentials flow into your infrastructure, you will need to provide it with the
following hooks in the options.hooks hash. You can see some [example CC hooks][] in the demo application.

#### grantClientToken({ clientId, clientSecret }, req, cb)

Checks that the API client is authorized to use your API, and has the correct secret. It should call back with a new
token for that client if so, or false if the credentials are incorrect. It can also call back with an error if there
was some internal server error while validating the credentials.

#### authenticateToken(token, req, cb)

Checks that a token is valid, i.e. that it was granted in the past by grantClientToken. It should call back with
true if so, or false if the token is invalid. It can also call back with an error if there was some internal
server error while looking up the token. If the token is valid, it is likely useful to set a property on the request
object indicating that so that your routes can check it later, e.g. req.authenticated = true or
req.clientId = lookupClientIdFrom(token).

$3

The idea behind this OAuth 2 flow is that your API clients will prompt the user for their username and password, and
send those to your API in exchange for an access token. This has some advantages over simply sending the user's
credentials to the server directly. For example, it obviates the need for the client to store the credentials, and
allows expiration and revocation of tokens. However, it does imply that you trust your API clients, since they will
have at least one-time access to the user's credentials.

To install Restify–OAuth2's resource owner password credentials flow into your infrastructure, you will need to
provide it with the following hooks in the options.hooks hash. You can see some [example ROPC hooks][] in the demo
application.

#### validateClient({ clientId, clientSecret }, req, cb)

Checks that the API client is authorized to use your API, and has the correct secret. It should call back with true
or false depending on the result of the check. It can also call back with an error if there was some internal server
error while doing the check.

#### grantUserToken({ clientId, clientSecret, username, password }, req, cb)

Checks that the API client is authenticating on behalf of a real user with correct credentials. It should call back
with a new token for that user if so, or false if the credentials are incorrect. It can also call back with an error
if there was some internal server error while validating the credentials.

#### authenticateToken(token, req, cb)

Checks that a token is valid, i.e. that it was granted in the past by grantUserToken. It should call back with
true if so, or false if the token is invalid. It can also call back with an error if there was some internal
server error while looking up the token. If the token is valid, it is likely useful to set a property on the request
object indicating that so that your routes can check it later, e.g. req.authenticated = true or
req.username = lookupUsernameFrom(token).

$3

Optionally, it is possible to limit the [scope][] of the issued tokens, so that you can implement an authorization
system in your application in addition to simple authentication.

#### grantScopes(credentials, scopesRequested, req, cb)

This hook is called after the token has been granted by authenticateToken. In the client credentials flow,
credentials will be { clientId, clientSecret, token }; in the resource owner password credentials flow, it will be
{ clientId, clientSecret, username, password, token }. In both cases, scopesRequested will be an array of the
requested scopes.

This hook can respond in several ways:

* It can call back with true to grant all of the requested scopes.
* It can call back with false to indicate that the requested scopes are invalid, unknown, or exceed the set of scopes
that should be granted to the given credentials.
* It can call back with an array to grant a different set of scopes.
* It can call back with an error if there was some internal server error while granting scopes.

In the cases of false or an internal server error, you should probably revoke the token before calling back, as the
server will send the user an error response, instead of a successful token grant.

$3

The hooks hash is the only required option, but the following are also available for tweaking:

* tokenEndpoint: the location at which the token endpoint should be created. Defaults to "/token".
* wwwAuthenticateRealm: the value of the "Realm" challenge in the WWW-Authenticate header. Defaults to
"Who goes there?".
* tokenExpirationTime: the value returned for the expires_in component of the response from the token endpoint.
Note that this is only the value reported; you are responsible for keeping track of token expiration yourself and
calling back with false from authenticateToken when the token expires. Defaults to Infinity.

What Does That Look Like?

OK, let's try something a bit more concrete. If you check out the [example servers][] used in the integration tests,
you'll see our setup. Here we'll walk you through the more complicated resource owner password credentials example,
but the idea for the client credentials example is very similar.

/

The initial resource, at which people enter the server.

* If a valid token is supplied in the Authorization header, req.username is truthy, and the app responds with
links to /public and /secret.
* If no token is supplied, the app responds with links to /token and /public.
* If an invalid token is supplied, Restify–OAuth2 intercepts the request before it gets to the application, and sends
an appropriate 400 or 401 error.

/token

The token endpoint, managed entirely by Restify–OAuth2. It generates tokens for a given client ID/client
secret/username/password combination.

The client validation and token-generation logic is provided by the application, but none of the ceremony necessary for
OAuth 2 conformance, error handling, etc. is present in the application code: Restify–OAuth2 takes care of all of that.

/public

A public resource anyone can access.

* If a valid token is supplied in the Authorization header, req.username contains the username, and the app uses
that to send a personalized response.
* If no token is supplied, req.username is null. The app still sends a response, just without personalizing.
* If an invalid token is supplied, Restify–OAuth2 intercepts the request before it gets to the application, and sends
an appropriate 400 or 401 error.

/secret

A secret resource that only authenticated users can access.

* If a valid token is supplied in the Authorization header, req.username is truthy, and the app sends the secret
data.
* If no token is supplied, req.username is null, so the application uses res.sendUnauthenticated() to send a nice
401 error with WWW-Authenticate and Link` headers.
* If an invalid token is supplied, Restify–OAuth2 intercepts the request before it gets to the application, and sends
an appropriate 400 or 401 error.

[Restify]: http://mcavage.github.com/node-restify/
[cc]: http://tools.ietf.org/html/rfc6749#section-1.3.4
[ropc]: http://tools.ietf.org/html/rfc6749#section-1.3.3
[token endpoint]: http://tools.ietf.org/html/rfc6749#section-3.2
[token-endpoint-success]: http://tools.ietf.org/html/rfc6749#section-5.1
[token-endpoint-error]: http://tools.ietf.org/html/rfc6749#section-5.2
[send-token]: http://tools.ietf.org/html/rfc6750#section-2.1
[token-usage-error]: http://tools.ietf.org/html/rfc6750#section-3.1
[oauth2-token-rel]: http://tools.ietf.org/html/draft-wmills-oauth-lrdd-07#section-3.2
[web-linking]: http://tools.ietf.org/html/rfc5988
[www-authenticate]: http://tools.ietf.org/html/rfc2617#section-3.2.1
[scope]: http://tools.ietf.org/html/rfc6749#section-3.3
[example ROPC hooks]: https://github.com/domenic/restify-oauth2/blob/master/examples/ropc/hooks.js
[example CC hooks]: https://github.com/domenic/restify-oauth2/blob/master/examples/cc/hooks.js
[example servers]: https://github.com/domenic/restify-oauth2/tree/master/examples