Why does adding Microsoft Identity auth cause another policy's GetTokenAsync("access_token") to return null?

Question

Problem:

I have an ASP.NET Core 3.1 web app with OpenIdConnect authentication. I added Microsoft Identity authentication (Azure Active Directory v2) on a separate (non-default) policy for use on one specific controller.

Adding Microsoft Identity with the following line (in Startup.cs) causes httpContext.GetTokenAsync("access_token") to return null, when called by a controller authorized with my original OpenIdConnect implementation. The httpContext being called still has all custom claims from the original OpenIdConnect implementation. Removing the below line fixes the issue and I can successfully get the Access Token.

services.AddMicrosoftIdentityWebAppAuthentication(Configuration, "AzureAd", "AzureAdOpenIdConnect", "AzureAdOpenIdCookies");

Other details:

The Microsoft Identity implementation is on a separate policy

services.AddAuthorization(options =>
{
    options.DefaultPolicy = new AuthorizationPolicyBuilder()
        .RequireAuthenticatedUser()
        .AddAuthenticationSchemes("oidcFlow") // scheme name for my original OpenIdConnect auth implementation
        .Build();

    options.AddPolicy("AzureAdOidc", new AuthorizationPolicyBuilder()
        .RequireAuthenticatedUser()
        .AddAuthenticationSchemes("AzureAdOpenIdConnect", "AzureAdOpenIdCookies") // scheme names used above when initializing Microsoft Identity
        .Build());
});

There are no controllers with the AzureAdOidc policy being called by the default policy controller that is attempting to get the Access Token.

Answer 1

UPDATE:

Moving the AddMicrosoftIdentityWebAppAuthentication call above the other auth implementation in ConfigureServices (in Startup.cs) fixed this issue, and I can obtain access tokens from calls authenticated with my other auth implemention again.