Visual Studio Code – Why do I get 'Sorry, there was an error' when trying to get Authentication code from Identity server 4?

I’m trying to implement an authorization code flow using Identity Server 4 but when I attempt to generate my authorization code all I get is a generic error page with nothing but the message ‘Sorry, there was an error’. (Title is ‘Error’).

I get this whether I’m using Postman or programmatically submitting a GET request with the required parameters.

To run my test, in Visual studio I start the Identity server and my API server. I start my MVC site to log in as the test user if needed and to make the callback url available. I then press the ‘Get New Access Token’ button in Postman. The result is that generic error.

I understand that when I programmatically submit the GET request the response should be the Auth Code which would be ideal but at this point I just want to successfully authenticate the client.

Can anyone see anything I might be missing?

In Postman my parameters are as follows in this image:

My Client is set up as follows:

            new Client
            {
                ClientId = "mvc",
                ClientSecrets = { new Secret("secret".Sha256()) },

                AllowedGrantTypes = GrantTypes.Code ,

                // where to redirect to after login
                RedirectUris = { "https://localhost:5002/signin-oidc" },

                // where to redirect to after logout
                PostLogoutRedirectUris = { "https://localhost:5002/signout-callback-oidc" },

                AllowOfflineAccess = true,
                AllowAccessTokensViaBrowser = true,

                AllowedScopes = new List<string>
                {
                    IdentityServerConstants.StandardScopes.OpenId,
                    IdentityServerConstants.StandardScopes.Profile,
                    "api1",
                    IdentityServerConstants.StandardScopes.Email
                }
            }

My test user is this one that comes with the Identity Server Github code:

                new TestUser
                {
                    SubjectId = "88421113",
                    Username = "bob",
                    Password = "bob",
                    Claims =
                    {
                        new Claim(JwtClaimTypes.Name, "Bob Smith"),
                        new Claim(JwtClaimTypes.GivenName, "Bob"),
                        new Claim(JwtClaimTypes.FamilyName, "Smith"),
                        new Claim(JwtClaimTypes.Email, "[email protected]"),
                        new Claim(JwtClaimTypes.EmailVerified, "true", ClaimValueTypes.Boolean),
                        new Claim(JwtClaimTypes.WebSite, "http://bob.com"),
                        new Claim(JwtClaimTypes.Address, JsonSerializer.Serialize(address), IdentityServerConstants.ClaimValueTypes.Json)
                    }
                }

My Startup for Identity Server:

public class Startup
{
    public IWebHostEnvironment Environment { get; }

    public Startup(IWebHostEnvironment environment)
    {
        Environment = environment;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        // uncomment, if you want to add an MVC-based UI
        services.AddControllersWithViews();

        services.AddAuthentication()
            .AddGoogle("Google", options =>
            {
                options.SignInScheme = IdentityServerConstants.ExternalCookieAuthenticationScheme;

                options.ClientId = "<insert here>";
                options.ClientSecret = "<insert here>";
            });

        services.AddAuthentication(IdentityServerAuthenticationDefaults.AuthenticationScheme)
            .AddIdentityServerAuthentication (options =>
            {
                options.Authority = "https://localhost:5001";
                options.ApiName = "testapis";
            });


        var builder = services.AddIdentityServer(options =>
        {
            // see https://identityserver4.readthedocs.io/en/latest/topics/resources.html
            options.EmitStaticAudienceClaim = true;
        })
        .AddDeveloperSigningCredential()        //This is for dev only scenarios when you don’t have a certificate to use.
        .AddInMemoryIdentityResources(Config.IdentityResources)
        .AddInMemoryApiScopes(Config.ApiScopes)
        .AddInMemoryClients(Config.Clients)
        .AddTestUsers(TestUsers.Users)
        .AddCustomTokenRequestValidator<CustomTokenRequestValidator>();

        // not recommended for production - you need to store your key material somewhere secure
        builder.AddDeveloperSigningCredential();
    }

    public void Configure(IApplicationBuilder app)
    {
        if (Environment.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        app.UseHttpsRedirection();
        //// uncomment if you want to add MVC
        app.UseStaticFiles();
        app.UseRouting();
        
        app.UseIdentityServer();
        app.UseAuthentication();

        //// uncomment, if you want to add MVC
        app.UseAuthorization();
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapDefaultControllerRoute();
        });
    }
}