Merged Diego's changes for OAuth2.0 server-side flow

src/main/java/org/scribe/builder/api/DefaultApi20.java

@@ -1,5 +1,6 @@
 package org.scribe.builder.api;
 
+import org.scribe.extractors.*;
 import org.scribe.model.*;
 import org.scribe.oauth.*;
 
@@ -22,6 +23,33 @@ import org.scribe.oauth.*;
 public abstract class DefaultApi20 implements Api
 {
 
+  /**
+   * Returns the access token extractor.
+   * 
+   * @return access token extractor
+   */
+  public AccessTokenExtractor getAccessTokenExtractor()
+  {
+    return new TokenExtractor20Impl();
+  }
+	
+  /**
+   * Returns the verb for the access token endpoint (defaults to GET)
+   * 
+   * @return access token endpoint verb
+   */
+  public Verb getAccessTokenVerb()
+  {
+    return Verb.GET;
+  }
+	
+  /**
+   * Returns the URL that receives the access token requests.
+   * 
+   * @return access token URL
+   */
+  public abstract String getAccessTokenEndpoint();
+	
   /**
    * Returns the URL where you should redirect your users to authenticate
    * your application.

src/main/java/org/scribe/builder/api/FacebookApi.java

@@ -5,8 +5,14 @@ import org.scribe.utils.*;
 
 public class FacebookApi extends DefaultApi20
 {
-  private static final String AUTHORIZE_URL = "https://graph.facebook.com/oauth/authorize?response_type=token&client_id=%s&redirect_uri=%s";
+  private static final String AUTHORIZE_URL = "https://www.facebook.com/dialog/oauth?client_id=%s&redirect_uri=%s";
 
+  @Override
+  public String getAccessTokenEndpoint()
+  {
+    return "https://graph.facebook.com/oauth/access_token";
+  }
+  
   @Override
   public String getAuthorizationUrl(OAuthConfig config)
   {

src/main/java/org/scribe/extractors/TokenExtractor20Impl.java

@@ -0,0 +1,35 @@
+package org.scribe.extractors;
+
+import java.util.regex.*;
+
+import org.scribe.exceptions.*;
+import org.scribe.model.*;
+import org.scribe.utils.*;
+
+/**
+ * Default implementation of {@AccessTokenExtractor}. Conforms to OAuth 2.0
+ *
+ */
+public class TokenExtractor20Impl implements AccessTokenExtractor
+{
+  private static final String TOKEN_REGEX = "access_token=(\\S*?)(&(\\S*))?";
+  private static final String EMPTY_SECRET = "";
+
+  /**
+   * {@inheritDoc} 
+   */
+  public Token extract(String response)
+  {
+    Preconditions.checkEmptyString(response, "Response body is incorrect. Can't extract a token from an empty string");
+
+    Matcher matcher = Pattern.compile(TOKEN_REGEX).matcher(response);
+    if (matcher.matches())
+    {
+      String token = URLUtils.percentDecode(matcher.group(1));
+      return new Token(token, EMPTY_SECRET);
+    } else
+    {
+      throw new OAuthException("Response body is incorrect. Can't extract a token from this: '" + response + "'", null);
+    }
+  }
+}

src/main/java/org/scribe/model/OAuthConstants.java

@@ -41,4 +41,9 @@ public class OAuthConstants
 
   //OAuth 2.0
   public static final String ACCESS_TOKEN = "access_token";
+  public static final String CLIENT_ID = "client_id";
+  public static final String CLIENT_SECRET = "client_secret";
+  public static final String REDIRECT_URI = "redirect_uri";
+  public static final String CODE = "code";
+  
 }

src/main/java/org/scribe/oauth/OAuth20ServiceImpl.java

@@ -35,7 +35,13 @@ public class OAuth20ServiceImpl implements OAuthService
    */
   public Token getAccessToken(Token requestToken, Verifier verifier)
   {
-    throw new UnsupportedOperationException("Unsupported operation, please use 'getAuthorizationUrl' and redirect your users there");
+    OAuthRequest request = new OAuthRequest(api.getAccessTokenVerb(), api.getAccessTokenEndpoint());
+    request.addQuerystringParameter(OAuthConstants.CLIENT_ID, config.getApiKey());
+    request.addQuerystringParameter(OAuthConstants.CLIENT_SECRET, config.getApiSecret());
+    request.addQuerystringParameter(OAuthConstants.CODE, verifier.getValue());
+    request.addQuerystringParameter(OAuthConstants.REDIRECT_URI, config.getCallback());
+    Response response = request.send();
+    return api.getAccessTokenExtractor().extract(response.getBody());
   }
 
   /**