Official documentation checked October 14, 2026.
HTTP 407 means the proxy requires authentication. It is different from a Microsoft account sign-in error or a certificate-validation failure. A repeated 407 can stop Copilot requests before they reach the service, but one challenge in a successful authentication exchange is not necessarily an error.
Start by identifying the exact client: organizational Copilot in a browser or Microsoft 365 app, or GitHub Copilot in an editor. These clients can have different proxy configuration and credential behavior. A browser that works does not prove that another application’s proxy authentication is configured correctly.
1. Capture the failed request without exposing credentials. Record the app/version, destination hostname, time, and whether the final response remains 407. Ask the network administrator to match it to proxy logs. The Proxy-Authenticate response header identifies the offered authentication method; it is not the same as a Microsoft sign-in requirement. Do not share authorization headers, cookies, passwords, or unredacted network captures. Microsoft’s HTTP authentication documentation explains the distinction between server 401 and proxy 407 responses.
2. Verify the intended proxy and authentication context. Have IT compare the affected app’s route with the approved proxy/PAC configuration. Check whether the request runs as the signed-in user or another process context and whether that client supports the offered authentication method. Do not respond to an unfamiliar proxy prompt with your organizational password until its destination is verified.
For a Windows component that actually uses WinHTTP, this command displays its basic configuration without changing it:
netsh winhttp show proxyThis does not display every app-specific or browser configuration. Do not automatically run a proxy reset: Microsoft documents that resetting changes WinHTTP to direct access, which may violate the intended route or break other services. See the WinHTTP command reference.
3. Apply the fix for the actual client. For a Microsoft 365 app, use the organization’s supported app updates and network configuration. Ask the proxy owner to resolve a rejected identity, incompatible authentication exchange, or incorrect rule for the documented service traffic. Keep TLS verification enabled; a CA import does not satisfy a 407 authentication challenge.
For GitHub Copilot, follow the editor-specific proxy instructions. GitHub documents different behavior for VS Code, JetBrains, and Visual Studio; Windows proxy settings do not automatically supply credentials in every editor. Prefer an organization-approved authentication method. Avoid putting a password into a command, URL, shared settings file, screenshot, or source repository even when a client permits that configuration.
4. Retest and record the outcome. Repeat the original Copilot action using non-sensitive input. Have IT confirm that proxy authentication completes and that the application request proceeds. A subsequent 401, 403, timeout, or TLS error is a new diagnostic result, not proof that the same 407 fix failed.
If the issue remains, provide sanitized request timing, client identity, destination, offered authentication scheme, and proxy-log outcome to support. Do not disable proxy authentication globally, broaden automatic credential forwarding, or clear unrelated Office credentials as a shortcut. Any network exception should be reviewed and scoped by the organization that operates the proxy.