Accessing User Profile

Now that the application has been issued an access token, it can use that token to make authenticated API requests. We'll explore how that is accomplished in this chapter.

Before we begin, it should be noted that the OAuth 2.0 protocol aspects of the sequence are complete. OAuth 2.0 is used to obtain authorization from the user (which was done with the authorization request and response) and exchange that authorization for an access token (which was done with the token request and response). At this point, the sequence is transitioning to use HTTP and the authentication features of that protocol.

Passport now makes a request to the Facebook Graph API, in particular the /me node, which returns data about the user whose access token is used to authenticate the API request:

GET /v3.2/me HTTP/1.1
Host: graph.facebook.com
Authorization: Bearer IAxLF5woqmfjTCHRD6gnp9X9RNVK3TG0

Note that the access token that was just issued is being used as a credential in the Authorization header. Because the token is a bearer token, it is utilized by simply including the access token string in the request according to the Bearer scheme, as specified by RFC 6750.

Just as different types of tokens can be returned in the OAuth 2.0 token response, the HTTP authentication framework allows for an extensible set of schemes that specify how to include credentials in a request. This guide only examines bearer tokens, as they are the most common token type in use today.

When Facebook receives this request, it verifies that the access token is valid and that the authorization granted permits access to the resource. If so, Facebook responds with information about the user.

HTTP/1.1 200 OK
Content-Type: application/json
     
{
  "name": "Alice Smith",
  "id": "14818013739641407"
}

Keep in mind that at this point Passport is still processing the authorization response using a route:

router.get('/oauth2/redirect/facebook', passport.authenticate('facebook', {
  successReturnToOrRedirect: '/',
  failureRedirect: '/login'
}));

The user request is interleaved in the middle of processing the authorization response, after the prior token request. A visualization of of the requests and responses that have occured up to this point looks as follows:

+-----+ <-- POST /oauth2/redirect/facebook --- +---------+
|     |                                        |         |
|     |   ----- Token Request  -----> +-----+  |         |
|     |   <---- Token Response ------ | AS  |  |         |
| App |                               +-----+  | Browser |
|     |   ------ User Request  -----> +-----+  |         |
|     |   <----- User Response ------ | API |  |         |
|     |                               +-----+  |         |
|     |   ...additional processing...          |         |
+-----+                                        +---------+

Now that Passport has obtained the user profile, it can authenticate the user.