What Is a Relying Party (RP)?

Updated on September 29, 2025

A Relying Party (RP) is a core component in a federated identity system that provides a service or application and relies on a trusted third party to authenticate a user. Rather than maintaining its own user database and authentication mechanism, the RP delegates that responsibility to an Identity Provider (IdP).

This model enables single sign-on (SSO), allowing users to access multiple applications with a single set of credentials. For developers and IT professionals, understanding the role of the RP is crucial for implementing secure, scalable applications in modern federated environments.

Definition and Core Concepts

A Relying Party is a web application or service that needs to control access to its resources and, to do so, relies on an external, trusted Identity Provider for user authentication. The RP trusts the IdP to verify a user’s identity and then sends a security token or assertion back to the RP. The RP then uses the claims within this token to make a decision about whether to grant access.

Foundational Concepts

• Identity Provider (IdP): The service that authenticates the user and issues the security token. Examples include corporate identity systems like Active Directory or public services like Google and Microsoft.
• Security Token: A digital credential issued by the IdP that contains verifiable claims about a user’s identity. Common formats include SAML and JWT.
• Trust Relationship: The core of federated identity. The RP and IdP must have a pre-established trust relationship where the RP is configured to accept tokens signed by the IdP.
• Claims: The specific assertions about the user (e.g., name, email, group membership) contained within the security token.

How It Works

The interaction between a Relying Party and an Identity Provider follows a standardized, secure protocol.

• Access Request: A user’s web browser attempts to access a protected resource on the Relying Party.
• Redirection to IdP: The RP recognizes the user isn’t authenticated and redirects the browser to the Identity Provider’s login page.
• Authentication: The user authenticates with the IdP using their credentials.
• Token Issuance: Upon successful authentication, the IdP generates a cryptographically signed security token containing the user’s claims.
• Return to RP: The IdP sends the user’s browser back to the RP, along with the security token.
• Token Validation: The RP receives the token. It does not try to re-authenticate the user. Instead, it validates the token’s signature using the IdP’s public key. If the signature is valid, the RP trusts the token.
• Access Granted: The RP extracts the claims from the token and uses them to grant the user access to the requested resource.

Key Features and Components

• Claim-Based: RPs are often referred to as “claims-aware” applications because they base their access control decisions on the claims within a security token.
• Outsourced Authentication: The RP offloads the complex and security-critical process of authentication to a dedicated IdP.
• Federated Identity: An RP is a necessary component of an identity federation, which allows users from one organization to securely access services in another.
• Trust Configuration: An RP must be explicitly configured with a trust relationship with a specific IdP. This configuration includes the IdP’s public key for signature validation and a unique identifier for the RP.

Use Cases and Applications

Relying Parties are ubiquitous in modern, cloud-based and enterprise environments.

• Corporate Applications: A company’s internal applications (e.g., a SharePoint site or a time tracking system) can be configured as RPs that rely on the corporate Active Directory Federation Services (ADFS) as the IdP.
• Cloud Services: Software as a Service (SaaS) applications like Salesforce and Office 365 act as RPs, allowing customers to use their existing corporate credentials to log in.
• Consumer Web: Websites that allow you to “log in with Google” or “sign in with Facebook” are acting as RPs, relying on those services as the IdP.

Advantages and Trade-offs

Advantages

Simplifies development and reduces the security burden on applications by eliminating the need to manage user credentials. It provides a seamless single sign-on (SSO) experience for users and centralizes identity management.

Trade-offs

The RP is highly dependent on the availability and security of the IdP. A failure in the IdP will prevent users from accessing the RP. The initial setup of the trust relationship can be complex, and a misconfiguration can lead to security vulnerabilities.

Key Terms Appendix

• Identity Provider (IdP): The service that authenticates users and issues security tokens.
• Single Sign-On (SSO): An authentication process that allows a user to access multiple applications with a single set of credentials.
• Federated Identity: The ability to link a user’s digital identity across different security domains.
• Security Token: A digital credential that contains verifiable claims about a user’s identity.
• Claims: The specific assertions about a user’s identity within a security token.