Windows Integration Errors

How to Fix cURL Error 0 During Azure AD Sign-In

Aamir Naveed Akram Oct 10, 2026 870 views

Question details

The user needs to resolve cURL error 0 that occurs during Microsoft Azure AD sign-in processes.

How to Fix cURL Error 0 During Azure AD Sign-In

Product: Microsoft Azure AD
Device & OS: not provided
Scenario: Attempting to authenticate or sign in using the Microsoft Azure identity token endpoint.
Observed behavior: The request to the token endpoint fails after repeated retries, returning cURL error 0, often because the client is unable to rewind the request body for another attempt.

Before you start

Before troubleshooting, ensure you have administrative access to your server's application code and network configuration settings. It is highly recommended to temporarily enable debug logging to capture detailed request and response data.

Solution 1Recommended

Enable Debug Logging and Verify Request Handling

Capture detailed error reports to identify the root cause of the cURL failure without exposing sensitive credentials.

cURL error 0 during token endpoint requests is often triggered by application logic failing to handle retry mechanisms correctly. Enabling verbose debugging will help pinpoint whether the request body stream is failing to rewind.

Enable cURL debug mode

Modify your application or cURL initialization settings to output verbose logs (e.g., setting CURLOPT_VERBOSE to true).

Review the retry logic

Examine the captured logs to check how the request body and retry logic are being handled, paying close attention to stream rewinding errors.

Sanitize your logs

Carefully remove any sensitive client secrets, access tokens, or user credentials from the logs before sharing them with your team or support.

Enable Debug Logging and Verify Request Handling

Protect Sensitive Data: Never expose your Azure AD secrets or tokens in public forums or unencrypted support emails when sharing debug reports.

Solution 2

Check Network Connectivity and TLS Settings

Ensure that your server's network allows uninterrupted, secure communication with Azure AD endpoints.

Solution 3

Contact Microsoft Support for Tenant-Level Investigation

Escalate the issue to Microsoft Support if local network and code configuration checks do not resolve the cURL error.

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Frequently Asked Questions

What does cURL error 0 mean during an Azure AD sign-in?

cURL error 0 generally means the request completed without a specific cURL-level failure code. However, in the context of Azure AD and SDKs, it frequently indicates an application-level failure where the client dropped the connection or could not rewind the request body stream for a retry attempt.

How can I safely share debug logs with Microsoft Support?

Before sharing any debug logs or network traces, you must manually sanitize the text by masking or removing sensitive information, including client secrets, authorization tokens, passwords, and identifiable user email addresses.

Why would my server fail to connect to login.microsoftonline.com?

Connection failures to Microsoft identity endpoints are typically caused by outdated CA certificate bundles on your server, restrictive outbound firewall rules, misconfigured proxy servers, or using deprecated TLS versions (like TLS 1.0 or 1.1) that Microsoft no longer supports.

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