The validity of the OAuth tokens used for authentication between Tableau Server and Azure AD When troubleshooting Azure AD authentication issues with Tableau Server, one of the first aspects to check is the validity of the OAuth tokens. These tokens are essential for the authentication process, and issues such as token expiration or invalidation can prevent successful authentication. Option A is incorrect because network bandwidth and speed, while important, are typically not the primary cause of authentication issues. Option C is incorrect as firewall settings, although they can block traffic, are less likely to be the specific cause of Azure AD authentication problems. Option D is incorrect because the version of the Azure AD module, while important, is not usually the first aspect to be checked in troubleshooting scenarios.