Redirect user to custom login page when using Azure AD

After some re going over the code I've found the solution to my issue.

Within Startup.Auth.cs:

app.UseCookieAuthentication(new CookieAuthenticationOptions {
   LoginPath = new PathString("/Account/Login")
});

app.UseOpenIdConnectAuthentication(
   new OpenIdConnectAuthenticationOptions {
      ClientId = clientId,
      Authority = authority,
      PostLogoutRedirectUri = postLogoutRedirectUri,
      AuthenticationMode = AuthenticationMode.Passive
});

It's the inclusion of the AuthenticationMode = AuthenticationMode.Passive line which seems to stop OpenIdConnectAuth from performing the automatic 302 redirect to the AAD login pages.