The described financial institution computing system provides services to customers through an application programming interface (“API”). The services include user identification services to customers. The user identification services allow the customers to verify the identity of users as non-fraudulent users. Further the user identification services allow the financial institution to provide known user information to the customers for purposes of prepopulating registration forms, completing transactions, and the like. Further services, such as user account validation services, payment services, and the like are also possible through the financial institution APIs. In some situations, users are registered with the financial institution. For example, a user may also be an account holder with the financial institution. In other situations, the users are not registered with the financial institution.