System and methods for user authentication across multiple domains

A system to support cross-domain user authentication, comprising:

• a first authentication agent associated with a first website/domain, which in operation, is configured to
• send a request for additional authentication information for a user attempting to login to the first website/domain to an authentication platform;
• return the additional authentication information provided to and entered by the user at the first website/domain to the authentication platform for verification;
• provide a signed cookie of authentication state of the user to a second web site/domain when the user is redirected to the second website/domain;
• a second authentication agent associated with said second website/domain, which in operation, is configured to
• parse the signed cookie for the additional authentication information and provide the additional authentication information to the authentication platform for verification;
• said authentication platform running on a computing unit, which in operation, is configured to
• create and return the signed cookie to be stored at the first website/domain once the additional authentication information received from the first website/domain is verified;
• verify the additional authentication information from the second website/domain and allow the user to access the second website/domain without entering any additional authentication information once verified.