slickorange

This simple plugin enables you to set up different access codes or passwords that enable users to be added to specific WordPress Roles or Press Permit (http://presspermit.com/) permission groups.
Simply go to Settings -> WP Access Codes to create and manage your codes.
Use the [wp-access-codes] shortcode to display the input field in the frontend.
More features planned! Please make your feature requests in the support area or send a mail to info@slickorange.co.za

WP Access Codes

Assigns a WordPress Role or/and a Press Permit Group to a user based on a predefined access code they enter.

Rapidweb

Edit user permissions for Ninja Forms.
By default, all Ninja Forms options are only available to users with the ‘Administrator’ role. This plugin will enable you to set which elements of Ninja Forms different user roles should have access to.

WP Access Codes vs Permissions Editor for Ninja Forms