Prototype pseudo-implementation of WebApplicationAuthorizationBuilder

WebApplicationAuthorizationBuilder.cs

public class WebApplicationAuthorizationBuilder
{
    private readonly WebApplicationBuilder _builder;

    public WebApplicationAuthorizationBuilder(WebApplicationBuilder builder)
    {
        _builder = builder;
    }

    public WebApplicationAuthorizationBuilder AddPolicy(
        string name,
        Action<AuthorizationPolicyBuilder> configurePolicy,
        bool setAsDefault = false,
        bool setAsFallback = false)
    {
        _builder.Services.AddAuthorization(authzOptions =>
        {
            var policyBuilder = new AuthorizationPolicyBuilder();
            configurePolicy(policyBuilder);
            var policy = policyBuilder.Build();
            
            authzOptions.AddPolicy(name, policy);
            
            if (setAsDefault)
            {
                authzOptions.DefaultPolicy = policy;
            }
            
            if (setAsFallback)
            {
                authzOptions.FallbackPolicy = policy;
            }
        });

        return this;
    }

    public WebApplicationAuthorizationBuilder SetDefaultPolicy(string name)
    {
        _builder.Services.AddAuthorization(authzOptions =>
        {
            if (authzOptions.GetPolicy(name) is AuthorizationPolicy policy)
            {
                authzOptions.DefaultPolicy = policy;
            }
            else
            {
                throw new InvalidOperationException($"Can't find policy named '{name}'.");
            }
        });

        return this;
    }

    public WebApplicationAuthorizationBuilder SetFallbackPolicy(string name)
    {
        _builder.Services.Configure<AuthorizationOptions>(authzOptions =>
        {
            if (authzOptions.GetPolicy(name) is AuthorizationPolicy policy)
            {
                authzOptions.FallbackPolicy = policy;
            }
            else
            {
                throw new InvalidOperationException($"Can't find policy named '{name}'.");
            }
        });

        return this;
    }

    public WebApplicationAuthorizationBuilder Configure(Action<AuthorizationOptions> configure)
    {
        _builder.Services.Configure(configure);

        return this;
    }
}

public static class WebApplicationBuilderExtensions
{
    private static readonly object _key = new();

    public static WebApplicationAuthorizationBuilder Authorization(this WebApplicationBuilder builder)
    {
        if (builder.Host.Properties.TryGetValue(_key, out var value) && value is WebApplicationAuthorizationBuilder authzBuilder)
        {
            return authzBuilder;
        }

        if (value is { })
        {
            throw new InvalidOperationException("There's a different object living in our slot!");
        }

        authzBuilder = new WebApplicationAuthorizationBuilder(builder);
        builder.Host.Properties.Add(_key, authzBuilder);
        return authzBuilder;
    }
}