The Microsoft Entra ID sign-in logs are the most direct and efficient tool for diagnosing user access issues. These logs capture detailed information about every interactive user sign-in attempt, including the user, the target application (Microsoft Defender for Cloud Apps), the status (success or failure), and the specific reason for any failure. An administrator can quickly filter the logs for User1's attempts to access the portal and identify the root cause, such as a Conditional Access policy block, an incorrect password, or a failed MFA prompt. This approach directly addresses the problem with the least administrative overhead.

A. Log Analytics: This is a more complex tool requiring data to be forwarded and queries to be written, which is not the most minimal administrative effort.

C. audit logs: These logs track administrative actions and configuration changes within the tenant, not user sign-in attempts.

D. provisioning logs: These logs track the automated creation, update, and deletion of user identities in applications, not interactive sign-in events.

1. Microsoft Learn. "Sign-in logs in Microsoft Entra ID." Microsoft Entra documentation. Accessed October 10

2023. In the "What can you do with it?" section

it explicitly states a key use case is to "Troubleshoot sign-in issues for a user." The documentation further details that the logs contain the "Sign-in error code" and "Failure reason" which are essential for diagnosing the problem.

2. Microsoft Learn. "Troubleshoot sign-in problems with Conditional Access." Microsoft Entra documentation. Accessed October 10

2023. This document demonstrates using the sign-in logs as the primary tool for troubleshooting access failures

stating

"The first place to look for more information is the Microsoft Entra sign-in logs... The sign-in log for the user should tell you why a user is or is not getting a prompt for MFA or why a policy is or is not applying."

3. Microsoft Learn. "Reporting and monitoring overview." Microsoft Entra documentation. Accessed October 10

2023. This overview clearly distinguishes the different log types. It describes sign-in logs for "information about the usage of managed applications and user sign-in activities

" while audit logs are for "system activity for users and groups

" and provisioning logs are for "system activity for applications." This confirms that sign-in logs are the correct choice for the described scenario.