Troubleshooting Lab: Select an appropriate authentication method
Diagnostic Scenarios
Scenario 1 — Root Cause
A support team receives calls from remote users reporting that they cannot establish VPN connections to the Azure infrastructure. The environment uses an Azure VPN Gateway configured with P2S and authentication via Microsoft Entra ID. The gateway was provisioned three weeks ago and was working normally until yesterday.
The administrator checks the portal and confirms that the gateway is in Running state. No changes were made to the gateway or the NSG rules associated with the gateway subnet. The administrator also confirms that the root certificate uploaded to the gateway has not expired.
One of the users sends the error displayed in the VPN client:
Error: The remote connection was not made because the attempted VPN tunnels failed.
Authentication failed. Verify your credentials and connection settings.
AADSTS70011: The provided request must include a 'redirect_uri' input parameter.
During the investigation, the administrator notices that a Microsoft Entra Conditional Access policy was updated yesterday afternoon by the security team. The administrator also verifies that one of the affected users' accounts is active and not blocked in Entra ID.
What is the root cause of the authentication failure?
A) The VPN client configuration package is outdated and needs to be regenerated after the gateway update
B) The updated Microsoft Entra Conditional Access policy is blocking the VPN application authentication flow
C) The user's client certificate has expired, preventing validation in Entra ID
D) The OpenVPN protocol was disabled on the gateway during automatic platform maintenance
Scenario 2 — Action Decision
The cause of the problem has been identified: the Azure VPN application registration in the corporate tenant's Microsoft Entra ID was accidentally deleted by an identity administrator during a cleanup routine of unused applications. The P2S environment with Entra ID authentication directly depends on this registration to issue OAuth 2.0 tokens.
The incident occurred in a production environment with approximately 300 active remote users. The planned maintenance window is next Friday, but the impact is already affecting critical operations. The identity team has Application Administrator permissions in Entra ID. There is no explicit backup of the application registration, but the retention period for deleted items in Entra ID is still active.
What is the correct action to take at this moment?
A) Wait for the maintenance window on Friday to recreate the application registration with documented configurations, avoiding unplanned changes in production
B) Restore the deleted application registration from the Microsoft Entra ID recycle bin, using the available Application Administrator permissions
C) Manually recreate a new application registration in Entra ID and update the VPN Gateway to point to the new App ID
D) Temporarily remove Entra ID authentication from the gateway and configure certificate authentication until the next maintenance window
Scenario 3 — Root Cause
An administrator configures a new P2S connection on an existing Azure VPN Gateway. The requirement is to authenticate users with digital certificates issued by the organization's internal CA. After configuration, some users can connect normally, while others receive the following message:
Error 812: The connection was prevented because of a policy configured
on your RAS/VPN server. Specifically, the authentication method used
by the server to verify your username and password may not match the
authentication method configured in your connection profile.
The administrator verifies and confirms:
- The internal CA root certificate was correctly uploaded to the VPN Gateway
- The gateway is configured to accept the SSTP protocol
- Users with failures are using Windows 11 with the native VPN client
- Users with success also use Windows 11 and the same native VPN client
- The gateway was updated from VpnGw1 to VpnGw2 SKU the previous week
The administrator suspects that the SKU update caused some incompatibility.
What is the root cause of the error in the affected users?
A) The SKU update from VpnGw1 to VpnGw2 changed protocol configurations and invalidated existing connection profiles
B) The client certificates of failing users were issued by an intermediate CA, and only the root certificate was uploaded to the gateway
C) The SSTP protocol is not supported in the VpnGw2 SKU, requiring migration to OpenVPN
D) Users with failures have the client certificate installed in the wrong Windows storage, outside the personal certificate repository
Scenario 4 — Diagnostic Sequence
An engineer receives a ticket: remote users cannot authenticate via P2S VPN using RADIUS integrated with on-premises Active Directory. The environment uses an on-premises NPS server reached via an existing Site-to-Site connection. The S2S connection is listed as Connected in the Azure portal.
The engineer has the following investigation steps available, presented out of order:
- Check NPS server logs to see if RADIUS requests are arriving and what response is being returned
- Confirm if the NPS server IP address is correctly configured as the RADIUS destination in the P2S VPN Gateway settings
- Test connectivity between the VPN Gateway and NPS server using the private IP (via ping or telnet on port 1812)
- Verify if the test user account is unlocked and has a valid password in Active Directory
- Confirm if the Site-to-Site connection between the VPN Gateway and on-premises network is in Connected state
What is the correct progressive diagnostic sequence?
A) 5 → 3 → 2 → 1 → 4
B) 2 → 5 → 3 → 1 → 4
C) 5 → 2 → 3 → 1 → 4
D) 4 → 5 → 2 → 3 → 1
Answer Key and Explanations
Answer Key — Scenario 1
Answer: B
The decisive clue in the statement is the error code AADSTS70011, which is an OAuth 2.0 flow error issued by Microsoft Entra ID, not by the gateway. This code indicates that the authentication flow was intercepted or rejected by Entra ID before completion, which is direct behavior of a Microsoft Entra Conditional Access policy that blocks or changes the authentication flow requirements for the VPN application.
The information about the non-expired root certificate is irrelevant in this scenario: authentication is via Entra ID with OpenVPN, and root certificates uploaded to the gateway are used in certificate authentication, not in Entra ID authentication. Including it in the statement exists to induce incorrect diagnosis.
Alternative A is incorrect because the symptom would be different and would not generate an AADSTS error. Alternative C is inconsistent with the configured authentication method (Entra ID does not validate client certificates). Alternative D would be easily detected in the portal and would generate a protocol error, not an OAuth authentication error.
The most dangerous distractor is A: regenerating the client package is a common troubleshooting action that would consume time without addressing the real cause.
Answer Key — Scenario 2
Answer: B
Microsoft Entra ID maintains deleted records in a recycle bin with a default retention period of 30 days. During this period, it's possible to restore the registration with all its original settings, including the App ID (client ID) already referenced by the VPN Gateway. The restoration doesn't require changes to the gateway, as the identifier remains the same.
Alternative A is technically defensible as a controlled change principle, but ignores that the impact is already in production and that a safe and non-destructive solution is available immediately. Waiting is the wrong decision when restoration via recycle bin is reversible and doesn't require a maintenance window.
Alternative C would force reconfiguration of the VPN Gateway with a new App ID, creating additional impact and error risk. Alternative D would change the authentication method for 300 users in production, would require certificate redistribution and would create a bigger problem than the original.
Answer Key — Scenario 3
Answer: B
Error 812 indicates that the certificate presented by the client was not validated by the trust chain configured on the gateway. When the internal CA uses an intermediate CA, the VPN Gateway needs both the root certificate AND the intermediate certificate to be uploaded separately. Uploading only the root certificate is insufficient to validate clients whose certificates were issued by the intermediate CA.
The clue that confirms this hypothesis is that some users connect successfully while others fail, with identical hardware and operating system. This eliminates any hypothesis related to the gateway (SKU, protocol) or operating system, as these causes would affect all users equally.
The information about the SKU update is irrelevant and purposefully included to mislead the diagnosis. SKU updates do not change authentication settings.
Alternative D (certificate in wrong storage) could cause similar symptoms, but error 812 is specific to certificate chain validation on the server, not certificate location on the client.
Answer Key — Scenario 4
Answer: C
The correct sequence is 5 → 2 → 3 → 1 → 4, which represents layered diagnosis, from outermost to innermost:
| Step | Action | Layer |
|---|---|---|
| 5 | Confirm S2S connection is Connected | Network connectivity |
| 2 | Confirm NPS IP in P2S settings | Gateway configuration |
| 3 | Test direct connectivity to NPS (port 1812) | Service reachability |
| 1 | Check NPS logs | Service behavior |
| 4 | Check user account in AD | Identity |
Without confirming network connectivity (step 5), any NPS investigation is premature. Without confirming gateway configuration (step 2), time could be wasted debugging the NPS server when traffic doesn't even reach it. Without testing port 1812 (step 3), a firewall blocking RADIUS would be invisible in NPS logs.
Alternative D starts with the user (step 4), which is the innermost layer and should only be investigated after confirming that network flow and configuration are correct. This sequence error would lead the engineer to validate credentials while RADIUS traffic doesn't even reach the server.
Troubleshooting Tree: Select an appropriate authentication method
Color Legend:
| Color | Node Type |
|---|---|
| Dark Blue | Initial symptom (entry point) |
| Blue | Diagnostic question |
| Red | Identified cause |
| Green | Recommended action or resolution |
To use this tree when facing a real problem, start with the root node (P2S authentication failure symptom) and answer each question based on what is observable in the environment: the configured authentication method, returned error codes, network connectivity state, and identity service behavior. Each branch eliminates hypotheses until isolating the cause or indicating the corrective action without ambiguity.