Fix issue WP-API#59, OAuth callback isn't called

Author: sblaz

lib/class-wp-json-authentication-oauth1.php

@@ -365,13 +365,14 @@ public function generate_request_token( $params ) {
 
 		// Generate token
 		$key = apply_filters( 'json_oauth1_request_token_key', wp_generate_password( self::TOKEN_KEY_LENGTH, false ) );
+		$callback = $params['oauth_callback'];
 		$data = array(
 			'key'        => $key,
 			'secret'     => wp_generate_password( self::TOKEN_SECRET_LENGTH, false ),
 			'consumer'   => $consumer->ID,
 			'authorized' => false,
 			'expiration' => time() + 24 * HOUR_IN_SECONDS,
-			'callback'   => null,
+			'callback'   => $callback,
 			'verifier'   => null,
 			'user'       => null,
 		);