Incidentally since 18 Apr 2023 a similar issue started occurring for me, however might be unrelated to your issue. I wasted days on investigating where GetConfigurationAsync within OWIN never yielded with no logged error/warning, see https://github.com/aspnet/AspNetKatana/blob/dbe159e43e2eee44f315f26268943e8ab5a4f60d/src/Microsoft.Owin.Security.OpenIdConnect/OpenidConnectAuthenticationHandler.cs#L148)
I finally found out that regardless of server best practice TLS configurations (which is TLS 1.2+), OWIN still contacts Microsoft's servers for pre-authentication configuration fetch (GetConfigurationAsync) via old TLS version (1.0 / 1.1)
Enforcement through machine registry entries will not work (will be ignored for unknown reasons). The only working method I found is to add to your application startup (Application_Start in Global.asax) a list of permitted TLS versions, like so
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls13 | SecurityProtocolType.Ssl3;
which is not recommended, since you lock-in the security protocols, but given the malfunction in the OWIN library a working trade-off.
Similar scenario: Anyway to restrict Owin HTTPS to TLS 1.2?