Login user based on the Gravity Form Submitted Data

login_submission_handler.php

<?php
/* part of a PHP Class */
public function login_form_after_submission($entry, $form) {
		// get the username or email and pass
		$username_or_email = $entry[1];
		$pass = $entry[3];
		$creds = array();
		// create the credentials array
		if( email_exists($username_or_email) ){
			$user = get_user_by( 'email', $username_or_email );
			$creds['user_login'] = $user->user_login;
		}
		else {
			$creds['user_login'] = $username_or_email;
		}

		$creds['user_password'] = $pass;
		// sign in the user and set him as the logged in user
		$sign = wp_signon( $creds );
		wp_set_current_user( $sign->ID );
	}