The subject disclosure relates to lightweight authentication for on-premise rich clients. The lightweight authentication mitigates the amount of software that is installed on a client machine for authentication purposes. A portion of an external website is hosted on an application executing on the rich client. The user can interact with the portion of the external website in order to enter credentials or other identification information. The entry of the credentials or other identification information is relayed to the external website for verification. If the verification is successful, the user can interact with various external websites utilizing the single verification.