Identity Provider (iDP) is a term often used in context to single sign-on (SSO). An identity provider is an organization which manages user account storage and authentication. Storing user credentials and handling user authentication requires very high security and therefore many companies prefer to outsource this part of the application/system to someone who are experts in this field and can offer a more secure solution.
Common identity providers are Facebook, Google, Twitter and Microsoft.
Most single sign-on services should work as long as their authentication system is based on OIDC (OpenID Connect) protocol. The following identity providers has been tested and verified to work in the portal: