The audience is invalid error

Question

I have 3 projects 1- Javascript SPA 2- Web API Project, 3- IdentityServer with EF Core

I started debugging API and Identity Server and successfully get the jwt token but, when I try to get value from API method which has Authorize Attribute I get an error:

WWW-Authenticate →Bearer error="invalid_token", error_description="The audience is invalid"

I could not found any property about audience in auth options. This is my configuration in API project

app.UseIdentityServerAuthentication(new IdentityServerAuthenticationOptions
        {
            ApiSecret="secret",
            Authority = "http://localhost:5000",
            ApiName="fso.Api",
            RequireHttpsMetadata = false,
        });

And my Config.cs file in Identity

 public class Config
{        
    public static IEnumerable<ApiResource> GetApiResources()
    {
        return new List<ApiResource>
        {                
            new ApiResource()
            {
                Name = "fso.Api",                    
                DisplayName = "feasion API",
                Scopes =
                {
                    new Scope("api1"),
                    new Scope(StandardScopes.OfflineAccess)
                },
                UserClaims =
                {
                    JwtClaimTypes.Subject,
                    JwtClaimTypes.EmailVerified,
                    JwtClaimTypes.Email,
                    JwtClaimTypes.Name, 
                    JwtClaimTypes.FamilyName,
                    JwtClaimTypes.PhoneNumber,
                    JwtClaimTypes.PhoneNumberVerified,
                    JwtClaimTypes.PreferredUserName,
                    JwtClaimTypes.Profile, 
                    JwtClaimTypes.Picture, 
                    JwtClaimTypes.Locale, 
                    JwtClaimTypes.IdentityProvider,
                    JwtClaimTypes.BirthDate, 
                    JwtClaimTypes.AuthenticationTime
                }
            }
        };
    }
    public static List<IdentityResource> GetIdentityResources()
    {
        return new List<IdentityResource>
        {
            new IdentityResources.OpenId(),
            new IdentityResources.Email(),
            new IdentityResources.Profile(),
        };
    }

    // client want to access resources (aka scopes)
    public static IEnumerable<Client> GetClients()
    {
        return new List<Client>
        {
            new Client
            {
                ClientId = "fso.api",
                AllowOfflineAccess=true,
                ClientSecrets =
                {
                    new Secret("secret".Sha256())
                },
                AllowedGrantTypes = GrantTypes.ResourceOwnerPassword,                    
                AllowedScopes =
                {                       
                   StandardScopes.OfflineAccess,                    
                   "api1"
                }
            }
        };
    }
}

Answer 1

See here for what this claim is about:

The aud (audience) claim identifies the recipients that the JWT is intended for. Each principal intended to process the JWT MUST identify itself with a value in the audience claim. If the principal processing the claim does not identify itself with a value in the aud claim when this claim is present, then the JWT MUST be rejected....

So your API's name must exist in the aud claim for the JWT to be valid when it is validated by the middleware in your API. You can use jwt.io to look at your token by the way, that can be useful to help make sense of it.

In order to have IdentityServer to add your API's name to the aud claim your client code (which is attempting to get a resource from the API and therefore needs an access token) should request a scope from your API. For example like this (from an MVC client):

app.UseOpenIdConnectAuthentication(new OpenIdConnectOptions
{
    Authority = Configuration["IdpAuthorityAddress"],
    ClientId = "my_web_ui_id",
    Scope = { "api1" },

    //other properties removed...
});