When trying to auto-link an account from an OpenID server to a built-in backend user Umbraco is throwing this error:

WARN  Umbraco.Web.Editors.BackOfficeController - Could not find external authentication provider registered: https://localhost:44333/identity

I'm not sure how it is even getting this provider or what it is matching against. This is my OWIN startup code:

        public void AutoLinkUp(BackOfficeIdentityUser curUser, ExternalLoginInfo loginDeets)
    {
        curUser.AccessFailedCount = 0;
    }

    public override void Configuration(IAppBuilder app)
    {
        //ensure the default options are configured
        base.Configuration(app);

        app.UseCookieAuthentication(new CookieAuthenticationOptions
        {
            AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie
        });

        var adOptions = new OpenIdConnectAuthenticationOptions
        { 
            Authority = "https://localhost:44333/identity",
            ClientId = "FYCU",
            RedirectUri = "https://localhost:44302",
            ResponseType = "id_token",
            Scope = "openid profile roles email",
            Caption = "Login now with CUID",

            SignInAsAuthenticationType = Umbraco.Core.Constants.Security.BackOfficeExternalAuthenticationType
        };

        adOptions.SetExternalSignInAutoLinkOptions(new ExternalSignInAutoLinkOptions(true, "CreditUnion")
        {
            OnAutoLinking = AutoLinkUp
        });

        adOptions.ForUmbracoBackOffice("btn-microsoft", "fa-windows");
        app.UseOpenIdConnectAuthentication(adOptions);      
    }