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Understanding Microsoft Access Token Validation

Summary

In many OAuth2/OpenID Connect workflows with Azure, access tokens are issued to clients for use against specific resources. This document summarizes the rationale behind token validation, when it is appropriate to perform it, and how different Microsoft services handle it.

Token Ownership: Who Should Validate?

According to Microsoft’s official documentation (source):

“An access token request involves two parties: the client, who requests the token, and the resource (Web API) that accepts the token. The resource that the token is intended for (its audience) is defined in the aud claim in a token. Clients use the token but shouldn’t understand or attempt to parse it. Resources accept the token.”

Conclusion:

• You should not attempt to validate or parse a token if you are the client.
• Only the intended resource should validate the access token.

Why Azure Management (AZ) Tokens Can Be Validated

Azure Management (e.g., https://management.azure.com) is a resource, just like Microsoft Graph. However:

• These tokens are often used in automation, scripts, or external apps.
• Azure’s public signing keys are available and consistent.
• Tokens follow open standards (JWT) and are signed with known keys retrievable from Azure AD’s JWKS endpoint.
• So, validation (e.g., via signature check) is feasible and sometimes useful, especially in CI/CD, logging, or diagnostics.

Use Cases Where AZ Token Validation Makes Sense

• Ensuring your automation isn’t passing expired or malformed tokens.
• Debugging authentication flows before making API calls.
• Auditing claims (e.g., tenant ID, app ID) in a secure and verifiable way.

How Microsoft Graph (MG) Validates Tokens Internally

When a request is made to MS Graph with a bearer token:

1. The token is extracted from the Authorization header.
2. MS Graph uses its internal trust system (backed by Azure AD) to:
   • Fetch signing keys (from Azure AD JWKS).
   • Verify the token’s cryptographic signature.
   • Confirm claims like aud, iss, exp, nbf, etc.

Why You Shouldn’t Validate MG Tokens Yourself

• Microsoft Graph is the resource — it owns the validation process.
• The client should treat the token as an opaque bearer token.
• Token structure may change and isn’t guaranteed to remain stable.
• Validating tokens client-side creates unnecessary security and compatibility risks.

Final Thoughts

• Validate Azure tokens if you control the resource or need introspection.
• Do not validate Microsoft Graph tokens client-side — let the Graph API handle it.

Treat tokens as bearer credentials, not application-owned data.