Added authorization URL to the Apis

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

@@ -1,7 +1,10 @@
 package org.scribe.builder.api;
 
+import org.scribe.model.Token;
+
 public class YammerApi extends DefaultApi10a
 {
+  private static final String AUTHORIZATION_URL = "'https://www.yammer.com/oauth/authorize?oauth_token=%s'";
 
 	@Override
 	public String getRequestTokenEndpoint()
@@ -14,5 +17,10 @@ public class YammerApi extends DefaultApi10a
   {
 		return "https://www.yammer.com/oauth/access_token";
 	}
-
+	
+	@Override
+	public String getAuthorizationUrl(Token requestToken)
+	{
+	  return String.format(AUTHORIZATION_URL, requestToken.getToken());
+	}
 }