Final answer:
The IdP endpoint accepting SOAP queries is defined by the Identity Provider (IdP) when configuring SAML.
Step-by-step explanation:
The correct answer is 3) Identity Provider (IdP). When configuring SAML (Security Assertion Markup Language), the IdP (Identity Provider) endpoint that accepts Simple Object Access Protocol (SOAP) queries is defined by the IdP itself. The IdP endpoint is the location where the Identity Provider receives and processes SAML requests, including SOAP queries. The Service Provider (SP) is the entity that relies on the IdP to authenticate users and provide access to resources, while SAML is the XML-based standard for exchanging authentication and authorization data between the IdP and the SP.