Archive Manager Autodiscover Fails with Error AADSTS7000218: The request body must contain ‘client_assertion’ or ‘client

Archive Manager Autodiscover Fails with Error AADSTS7000218: The request body must contain ‘client_assertion’ or ‘client_secret’ (4381257)

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Title

Archive Manager Autodiscover Fails with Error AADSTS7000218: The request body must contain ‘client_assertion’ or ‘client_secret’
Description
Archive Manager fails to authenticate to Exchange Online during Autodiscover or EWS connection attempts.

The AM log shows:

Microsoft.Identity.Client.MsalServiceException: A configuration issue is preventing authentication.

AADSTS7000218: The request body must contain the following parameter: 'client_assertion' or 'client_secret'.

Correlation ID: <ID>

Timestamp: <Date Time>

Symptoms include:
- Autodiscover test fails
- EWS login test fails
- Indexing job cannot retrieve mailbox items
- Authentication attempts fail immediately at MSAL level
Cause

The Azure App Registration used by Archive Manager is configured as a Public Client, but the setting Allow Public Client Flows is disabled.

Archive Manager uses the ROPC (Resource Owner Password Credentials) authentication flow, which only works if Azure permits public client flows.
When this setting is disabled, Azure requires a client_secret, which AM does not provide, resulting in error AADSTS7000218.
Resolution
Enable Public Client Flows in Azure
1. Open Azure Portal : https://entra.microsoft.com/
2. Go to App registrations > All application > ArchiveManager > Authentication
3. Under Advanced settings, enable: Allow public client flows
4. Enable the following mobile and desktop flows: →YES
5. Click Save
Retry Autodiscover / EWS in Archive Manager
1. Open Archive Manager Configuration
2. Go to Autodiscover / Modern Authentication settings
3. Click Test
4. Ensure the authentication completes successfully
Restart Archive Manager Services (if needed)

If indexing or search is already running, restart:
- AM Indexing Service
- AM Search Service
Result:

After enabling public client flows, Archive Manager successfully authenticates using modern auth, resolving error AADSTS7000218, and mailbox processing resumes normally.

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Archive Manager Autodiscover Fails with Error AADSTS7000218: The request body must contain ‘client_assertion’ or ‘client_secret’ (4381257)

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