Fix typo `CSFR` -> `CSRF` in the OAuth2 doc

doc/api/oauth2.md

@@ -4,7 +4,7 @@ This document covers using the OAuth2 protocol to access GitLab.
 
 If you want GitLab to be an OAuth authentication service provider to sign into other services please see the [Oauth2 provider documentation](../integration/oauth_provider.md).
 
-OAuth2 is a protocol that enables us to authenticate a user without requiring them to give their password to a third-party. 
+OAuth2 is a protocol that enables us to authenticate a user without requiring them to give their password to a third-party.
 
 This functionality is based on [doorkeeper gem](https://github.com/doorkeeper-gem/doorkeeper)
 
@@ -22,7 +22,7 @@ In the following sections you will be introduced to the three steps needed for t
 ### 1. Registering the client
 
 First, you should create an application (`/profile/applications`) in your user's account.
-Each application gets a unique App ID and App Secret parameters. 
+Each application gets a unique App ID and App Secret parameters.
 
 >**Note:**
 **You should not share/leak your App ID or App Secret.**
@@ -46,10 +46,10 @@ http://myapp.com/oauth/redirect?code=1234567890&state=your_unique_state_hash
 You should then use the `code` to request an access token.
 
 >**Important:**
-It is highly recommended that you send a `state` value with the request to `/oauth/authorize` and 
-validate that value is returned and matches in the redirect request. 
-This is important to prevent [CSFR attacks](http://www.oauthsecurity.com/#user-content-authorization-code-flow), 
-`state` really should have been a requirement in the standard! 
+It is highly recommended that you send a `state` value with the request to `/oauth/authorize` and
+validate that value is returned and matches in the redirect request.
+This is important to prevent [CSRF attacks](http://www.oauthsecurity.com/#user-content-authorization-code-flow),
+`state` really should have been a requirement in the standard!
 
 ### 3. Requesting the access token
 
@@ -62,7 +62,7 @@ RestClient.post 'http://localhost:3000/oauth/token', parameters
 # The response will be
 {
  "access_token": "de6780bc506a0446309bd9362820ba8aed28aa506c71eedbe1c5c4f9dd350e54",
- "token_type": "bearer", 
+ "token_type": "bearer",
  "expires_in": 7200,
  "refresh_token": "8257e65c97202ed1726cf9571600918f3bffb2544b26e00a61df9897668c33a1"
 }
@@ -95,7 +95,7 @@ curl --header "Authorization: Bearer OAUTH-TOKEN" https://localhost:3000/api/v3/
 
 ---
 
-In this flow, a token is requested in exchange for the resource owner credentials (username and password). 
+In this flow, a token is requested in exchange for the resource owner credentials (username and password).
 The credentials should only be used when there is a high degree of trust between the resource owner and the client (e.g. the
 client is part of the device operating system or a highly privileged application), and when other authorization grant types are not
 available (such as an authorization code).