Exchange Token Validation Error with a JWT from Exchange Microservice

Question

Hello! I am struggling with the validation of the Exchange Token. The documented process on how to validate the token worked for a long time but does not anymore. Please see "Validate token contents" here Office 365 Exchange MicroserviceOffice 365 Exchange Microservice for the documentation. I assume the validation failed due to the missing x5t in https://outlook.office365.com/autodiscover/metadata/json/1 The error is: IDX10501: Signature validation failed. Unable to match key: kid: 'System.String'. Exceptions caught: 'System.Text.StringBuilder'. token: 'System.IdentityModel.Tokens.Jwt.JwtSecurityToken' It is obious that something changed. The JWT says that the app is "Office 365 Exchange Microservice" now. I would be grateful if you could give me a hint how to validate the new JWT from the Exchange Microservice. Best regards
Paul

Answer 1

Hi Paul,

If the JWT you’re trying to validate lacks the x5t parameter, it might be due to changes in the token generation process or the certificate used. The absence of x5t could lead to signature validation failures, as you’ve observed.

The absence of x5t might indicate a change in the token generation process. Ensure that the certificate used for signing is correctly configured.

You may need validate the new JWT from the Exchange Microservice - retrieving the public key, checking the thumbprint and verifying the signature.