Difference between STS and Identity Provider (IdP)

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I was trying to implement Ws-Federation protocol for my application. When researching for this STS and IdP are used along with few other buzzwords. I know Federation is between two security realm to trust each other to access resource. And IdP was the source of identity about the user and IdP's can use SAML , OAUTH , OIDC and others during authentication of the user. What role does STS play here. Explain all Buzzwords like IdPs, SPs , relying party , Federation and STS in much more clear way and with some analogy Thanks.

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rbrayb On

In the Microsoft world (since you are asking about WS-Fed):

  • IDP - handles authentication and issues tokens, either SAML or JWT (OIDC). Examples are ADFS or Entra ID. (WS-Fed issues SAML tokens)

  • CP - claims provider - the instance in the IDP that handles a particular RP request. In ADFS, this would run the claims rules

  • RP - The application, e.g. ASP.NET, that connects to the CP via WS-Fed

  • SP - this is the equivalent of an RP in the SAML world

  • Federation - connecting two IDPs together so, e.g. users in an ADFS tenant can authenticate to an Entra ID application

  • STS - security token system - the part of an IDP that issues tokens

I have also seen STS used as an intermediary IDP, e.g. RP --> ADFS --> Entra ID as opposed to RP --> Entra ID. The ADFS here would be the STS.