Unable to authenticate to REST API after service account credential reset

Hi @Malzaar

Based on the scenario, the issue is most likely related to the application continuing to use expired or outdated credentials/tokens after the service account password, secret, or authentication token was reset.

1. Verify how the application stores credentials

The first step is to determine how the Windows application authenticates to the REST API:

• Windows Service Logon Account
• Stored username/password in a configuration file
• Windows Credential Manager
• API key
• OAuth access token and refresh token
• Certificate-based authentication

If credentials are stored locally (for example in a configuration file, encrypted store, or Credential Manager), update them with the newly issued credentials and restart only the affected service if required.

2. Update the Windows Service Account Password

If the service runs under a domain or local service account whose password was reset:

1. Open Services (services.msc).
2. Locate the service.
3. Open Properties → Log On.
4. Re-enter the updated password for the service account.
5. Apply the changes.
6. Restart the service.

This updates the Service Control Manager's stored credentials without requiring a server reboot.

3. Verify Application Tokens or API Secrets

If the application uses:

• OAuth Client Secret
• Bearer Token
• API Key
• Service Principal Secret

ensure the new secret or token has been updated in:

• Application configuration files
• Registry settings
• Secret stores
• Azure Key Vault (if used)
• Environment variables

Also verify that any cached tokens are refreshed after the credential change.

4. Review Windows Event Logs

The following logs are typically useful when troubleshooting authentication failures:

Event Viewer

Windows Logs → Application

• Application-specific authentication errors
  • .NET exceptions
    • API authentication failures
    Windows Logs → Security

    - Logon failures
    
       - Account lockouts
    
          - Credential validation issues
    
          **Windows Logs → System**
    
             - Service startup failures
    
                - Service account logon problems
    

Common Security Event IDs

• 4625 – Failed logon
• 4648 – Logon attempted using explicit credentials
• 4771 – Kerberos pre-authentication failure
• 4776 – Credential validation failure

5. Check Service-Specific Logs

Many Windows applications write their own logs under:

Plain Text

C:\ProgramData<ApplicationName>\Logs

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or

Plain Text

C:\Logs

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Look for messages such as:

Plain Text

401 Unauthorized

403 Forbidden

Invalid Token

Token Expired

Authentication Failed

Access Denied

Invalid Client Secret

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6. Test the API Independently

To isolate whether the issue is with the application or the credentials:

PowerShell

Invoke-RestMethod `

-Uri "https://api.example.com" `

-Headers @{ Authorization = "Bearer <token>" }

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or test using Postman with the newly issued credentials.

If the API call succeeds externally but fails from the application, the application is likely still using cached or outdated credentials.

Thanks.

Hello,

When a Windows-based service loses connectivity to an external REST API after a service account credential reset, the most direct fix is to update the stored credentials or token in the context where the application is running. If the service is configured to run under a Windows service account, you need to re-enter the updated password in Services.msc. Open the service properties, go to the Log On tab, and reapply the new credentials. This ensures the Windows Service Control Manager can authenticate the account at startup. If the application itself stores an API token or credential in its configuration, you must update that in the application’s config file or registry location (commonly under HKLM\Software\<Vendor>\<AppName> or in %ProgramData%\<AppName>\config.json). Without this, the service will continue attempting to use the expired token.

For REST API tokens specifically, many applications cache them either in memory or in a local secure store. If the token was reset by the API provider, you’ll need to request a new token from the provider’s authentication endpoint and replace it in the application’s configuration. Restarting the service after updating the credentials is usually required, but this does not impact the rest of the system.

To identify the authentication failure, check Windows Event Viewer under Windows Logs > Application for .NET or application-specific errors, and under Windows Logs > Security for failed logon attempts tied to the service account. Additionally, the System log will show Event ID 7000 or 7011 if the service fails to start due to bad credentials. If the application writes its own logs, review those for HTTP 401/403 responses from the REST API, which confirm authentication rejection.

If you are unsure whether the application is using Windows service account credentials or an API token stored separately, I recommend clarifying which authentication method is in place. That will determine whether you need to reset the Windows service logon credentials or update the API token in the application’s configuration.

I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!

HP.