Add Foursquare2 API and example

src/main/java/org/scribe/builder/api/Foursquare2Api.java

@@ -0,0 +1,29 @@
+package org.scribe.builder.api;
+
+import org.scribe.extractors.*;
+import org.scribe.model.*;
+import org.scribe.utils.*;
+
+public class Foursquare2Api extends DefaultApi20
+{
+  private static final String AUTHORIZATION_URL = "https://foursquare.com/oauth2/authenticate?client_id=%s&response_type=code&redirect_uri=%s";
+
+  @Override
+  public String getAccessTokenEndpoint()
+  {
+    return "https://foursquare.com/oauth2/access_token?grant_type=authorization_code";
+  }
+
+  @Override
+  public String getAuthorizationUrl(OAuthConfig config)
+  {
+    Preconditions.checkValidUrl(config.getCallback(), "Must provide a valid url as callback. Foursquare2 does not support OOB");
+    return String.format(AUTHORIZATION_URL, config.getApiKey(), URLUtils.formURLEncode(config.getCallback()));
+  }
+
+  @Override
+  public AccessTokenExtractor getAccessTokenExtractor()
+  {
+    return new JsonTokenExtractor();
+  }
+}