code: private String _getAuthorizationUrl(String oauthCallback) {
  		String url = null;
          
  		try {
              url = mOAuthProvider.retrieveRequestToken(mOAuthConsumer, oauthCallback);
          }
          catch (OAuthException e) {
              e.printStackTrace();
          }
  		
  		return url;
  	}
docs: Get authorization URL, use provided callback URL
  
  @param   oauthCallback URL, i.e. oauth_callback
  @return	URL for authorizing application