Open the sign-in page in an InPrivate/incognito window with extensions and VPN/proxy disabled; this exact post_request_failed symptom is most commonly resolved by removing browser privacy or network filtering from the authentication request.^1^

If you cannot access the Azure portal

Test in this order:

1. Open a private browsing window and sign in again.
2. Temporarily disable ad blockers, privacy extensions, and other browser extensions.
3. Allow third-party cookies for the sign-in attempt.
4. Disconnect any VPN or corporate proxy.
5. Try another browser and then a different network, such as a mobile hotspot.

If another browser or network works, the issue is likely local browser or network filtering. Ask the network administrator to inspect firewall/proxy filtering of Microsoft sign-in traffic rather than changing the Azure account.

post_request_failed is an MSAL error classification, not enough by itself to establish a tenant, password, or App Service problem. MSAL errors are intended to expose details for troubleshooting, so capture the complete error object and the failed request from Developer tools → Network if the tests above do not isolate it.^2^

If this occurs inside your own App Service application

These configuration checks apply only to the application's sign-in page, not to signing in directly at the Azure portal.

Browser-based MSAL application

If the browser console reports CORS, or the frontend uses @azure/msal-browser/@azure/msal-react:

1. Go to Microsoft Entra ID → App registrations → your application → Authentication.
2. Find the exact redirect URI used by the application.
3. Verify that it is registered under the Single-page application (SPA) platform, not only under Web.
4. Ensure the URI matches exactly, including scheme, host, path, and port.
5. Save and retry in a private window.

The SPA platform check is specifically relevant to browser MSAL and CORS-style failures.^3^

Only if logs show redirect handling is incomplete or overlapping interactive calls, await handleRedirectPromise() before starting another login:

const response = await msalInstance.handleRedirectPromise();

if (!response) {
    const accounts = msalInstance.getAllAccounts();
    if (accounts.length === 0) {
        await msalInstance.loginRedirect({
            scopes: ["openid", "profile"]
        });
    }
}

MSAL requires redirect processing to complete before another interactive operation begins.^4^

App Service built-in Authentication (“Easy Auth”)

If App Service performs the authentication rather than the SPA:

1. Open App Service → Authentication and select the Microsoft identity provider.
2. Identify the app registration and credential used by that provider.
3. In Microsoft Entra ID → App registrations → your application → Certificates & secrets, check whether that client secret is expired or no longer matches the configured credential.
4. If expired or mismatched, create a new client secret.
5. Return to App Service → Authentication → Microsoft identity provider, replace the configured secret with the new value, save, and retry.

Treat the new secret value as sensitive; it is displayed only when created. An invalid or expired credential can prevent the server-side authorization-code exchange.^5^

If none of these paths resolves it, collect the browser, operating system, affected URL, full MSAL error, failed Network request, and whether the problem occurs on another network. Those details distinguish portal access from SPA or Easy Auth failures.

References

1. Acceso Azure - Microsoft Q&A
2. Handle errors and exceptions in MSAL.js - learn.microsoft.com
3. BrowserAuthError: post_request_failed: Network request failed: If the ...
4. Common errors in MSAL JS - Microsoft Authentication Library for ...
5. How to fix this error - Microsoft Q&A