Update getting-started.md

doc/api/pages/getting-started.md

@@ -31,13 +31,51 @@ fetch('/api/v2/tokens', {
   credentials: 'same-origin'
 }).then(response => {
   return response.json()
-}).then(payload => {
-  console.log(payload)
-}).catch(console.error)
+}).then(console.log).catch(console.error)
 ```
 
 `payload.data.token` will contain a string which you can use to append to requests to access the API from anywhere.
 
 ### 3. OAuth 2 Authentication
 
-TODO
+We use a flow for Oauth 2 authentication called Authorization Code. It basically consists of an exchange of an `authorization` token for an `access token`. For more detailed info, check out the [RFC spec here](http://tools.ietf.org/html/rfc6749#section-4.1)
+
+The first step is to register your client app.
+
+#### Registering the client
+
+Set up a new client in `/oauth/applications/new`. For testing purposes, you should fill in the redirect URI field with `urn:ietf:wg:oauth:2.0:oob`. This will tell it to display the authorization code instead of redirecting to a client application (that you don't have now).
+
+#### Requesting authorization
+
+To request the authorization token, you should visit the `/oauth/authorize` endpoint. You can do that either by clicking in the link to the authorization page in the app details or by visiting manually the URL:
+
+```
+http://metamaps.cc/oauth/authorize?client_id=YOUR_CLIENT_ID&redirect_uri=urn:ietf:wg:oauth:2.0:oob&response_type=code
+```
+
+Once you are there, you should sign in and click on `Authorize`.
+You will then see a response that contains your "authorization code", which you need to exchange for an access token.
+
+#### Requesting the access token
+
+To request the access token, you should use the returned code and exchange it for an access token. To do that you can use any HTTP client. Here's an example with `fetch`
+
+```javascript
+fetch('https://metamaps.cc/oauth/token?client_id=THE_ID&client_secret=THE_SECRET&code=RETURNED_CODE&grant_type=authorization_code&redirect_uri=urn:ietf:wg:oauth:2.0:oob', {
+  method: 'POST',
+  credentials: 'same-origin'
+}).then(response => {
+  return response.json()
+}).then(console.log).catch(console.error)
+
+# The response will be like
+{
+ "access_token": "de6780bc506a0446309bd9362820ba8aed28aa506c71eedbe1c5c4f9dd350e54",
+ "token_type": "bearer", 
+ "expires_in": 7200,
+ "refresh_token": "8257e65c97202ed1726cf9571600918f3bffb2544b26e00a61df9897668c33a1"
+}
+```
+
+You can now make requests to the API with the access token returned.