Forum Discussion
Microsoft Edge Enterprise — Intermittent Blue Coat Proxy Authentication Prompt
Product: Microsoft Edge for Business / Microsoft Edge Enterprise
Component: Proxy authentication, HTTP networking and integrated authentication
Operating system: Windows 11 Enterprise Proxy: Blue Coat / Broadcom forward proxy, port 8080
Proxy authentication configuration: Basic Auth/ IWARealm exact authentication method to be confirmed
Affected browser: Microsoft Edge for Business
Comparison browser: Mozilla Firefox, where the same behaviour has not been observed
Impact: Intermittent interruption of browsing and loss of access to existing tabs until the user reauthenticates
We are experiencing intermittent, unexpected proxy authentication prompts in Microsoft Edge for Business. The dialog states: Sign in to access this site. The proxy http://[bluecoat-host-url]:8080 requires a username and password. Your connection to this site is not secure. The prompt appears sporadically, sometimes while the browser is idle or while tabs displaying otherwise idle ServiceNow, deepl etc. pages cannot be accessed until user reauthenticates with autofill if proxy password is saved in order to be able to access those sites again. No explicit navigation or user interaction is necessarily taking place when the dialog appears. This behaviour was not observed previously and has become noticeable more recently especially since the migration of a lot of our workloads to the microsoft cloud. Firefox does not appear to exhibit the same symptom under comparable.
We suspect that a background request, a new or reused proxy connection, proxy-session reauthentication, or an incomplete integrated-authentication exchange may be triggering the prompt. However, we have not yet identified the exact request or established whether the root cause is Edge, the proxy configuration, PAC routing, or the authentication infrastructure. usage conditions.
Edge should silently authenticate to the configured enterprise proxy through the organisation's approved authentication mechanism, without unexpectedly displaying a credential prompt during normal browsing or background activity.
1 Reply
Your screenshot shows a proxy credential dialog, not a Microsoft account sign-in prompt. The key missing fact is whether Blue Coat is actually advertising Basic, Negotiate, or NTLM when the interruption occurs. Microsoft documents repeated proxy challenges when routing or authentication exchanges fail; an intermediate 407 during Negotiate is not automatically a failure. Capture one occurrence with Edge’s network export facility and correlate its timestamp with the proxy authentication logs. Check effective ProxySettings and PAC routing for the triggering request, including background subresources, then have the proxy administrator confirm the offered scheme. If integrated authentication is intended, review AuthSchemes, the proxy hostname, SPN, and Kerberos tickets together. Do not widen authentication allowlists indiscriminately or enable Basic authentication over an unprotected HTTP connection as a workaround. Firefox behaving differently is useful comparison evidence, but does not alone prove an Edge defect.
