Token endpoint path should be fetched from issuer's openid configuration (.well-known/openid-configuration) endpoint. AzureAD has oauth2/token for instance and OAuth2Client is unable to fetch access token using client credentials flow (FgaApiNotFoundError exception is thrown). https://github.com/openfga/dotnet-sdk/blob/main/src/OpenFga.Sdk/ApiClient/OAuth2Client.cs#L122