c# How to use Oauth/OpenId between containerized projects?

Let's say I do have two projects that are containerized in Docker.

Project A - is already existing with some kind of OAuth implemented that is reaching Enterprise App registration within Azure AD (work account). I would like to not touch/change this project if possible.

Project B - is a REST API that I need to partially secure (part of endpoints will be still publicly/anonymously available). I don't care about policies/roles/claims - I wan't this super simple for beginning - whenever someone logged successfully in Project A, should be able to access any authorized endpoint in Project B.

Here is how the authentication is done in Project A:

services.AddAuthentication(options => {
        options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = OpenIdConnectDefaults.AuthenticationScheme;
    })
    .AddCookie()
    .AddOpenIdConnect(options =>
    {
        options.ClientId = authSettings.AppId;
        options.ClientSecret = authSettings.AppSecret;
        options.MetadataAddress = $"https://login.microsoftonline.com/{authSettings.TenantId}/v2.0/.well-known/openid-configuration?appid={authSettings.AppId}";
        options.Authority = $"https://login.microsoftonline.com/{authSettings.TenantId}/oauth2/v2.0";
        options.ResponseType = "code";
        options.GetClaimsFromUserInfoEndpoint = true;
        options.TokenValidationParameters = new TokenValidationParameters {
            NameClaimType = "name"
        };
    });

services.AddAuthorization(options => {
    options.FallbackPolicy = new AuthorizationPolicyBuilder()
        .RequireAuthenticatedUser()
        .Build();
});

My questions are:

1. How should I setup Project B to use information about authentication that was done in Project A?
2. How should I pass that information from Project A to Project B along the request?