The correct answer is Proxy relay. In a federated authentication exchange that role is not one of the three primary parties which are the User the Identity provider and the Relying party.

Proxy relay is not a standard participant in SAML or OpenID Connect. A proxy or relay may appear as an intermediary component that forwards messages or manages network traffic but it is not counted as one of the three principal parties that perform authentication and token or assertion exchange.

Relying party is incorrect because the relying party is a primary participant that consumes assertions or tokens and relies on the identity provider to authenticate the user. It is often called the service provider in SAML and the client in OAuth and OpenID Connect.

User is incorrect because the user or principal initiates the authentication and is one of the three core parties in any federated authentication flow.

Identity provider is incorrect because the identity provider issues authentication assertions or tokens and vouches for the user, making it a primary participant in federated exchange.

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