AccessToken does miss critical audience after update to IdentityServer4 3.1.3 - identityserver4

Question

We've implemented an Identity-Provider using IdentityServer4. Recently we upgraded the application to .net core 3.1 (from 2.1) and with it, we upgraded IdentityServer4-Nuget-Packages from Version 2.2.0 to 3.1.3.
These are the actual contents of an access-token provided by the old state (with .net 2.1 and IdentityServer4 2.2.0)
{
"nbf": 1597236398,
"exp": 1597239998,
"iss": "https://lab10vm-tri-2:8777/usermgmt/identityprovider",
"aud": [
"https://lab10vm-tri-2:8777/usermgmt/identityprovider/resources",
"basecommon"
],
"client_id": "Webportal",
"sub": "d860efca-22d9-47fd-8249-791ba61b07c7",
"auth_time": 1597236392,
"idp": "local",
"upn": "Administrator",
"scope": [
"openid",
"profile",
"basecommon"
],
"amr": [
"pwd"
]
}
And these are the contents of an access-token provided by the new state (with .net 3.1 and IdentityServer4 3.1.3):
{
"nbf": 1597236389,
"exp": 1597239989,
"iss": "https://lab10vm-tri-3:8777/usermgmt/identityprovider",
"aud": "basecommon",
"client_id": "Webportal",
"sub": "d860efca-22d9-47fd-8249-791ba61b07c7",
"auth_time": 1597236383,
"idp": "local",
"upn": "Administrator",
"scope": [
"openid",
"profile",
"basecommon"
],
"amr": [
"pwd"
]
}
As you can see, the old version contains an audience called "https://lab10vm-tri-2:8777/usermgmt/identityprovider/resources", and the newer version does not.
Please tell me: how I can restore the behaviour from before so that the audience is attached?
What I've tried: Google, very, very much on topics like "IdentityServer 3.1 audience missing" and such.
All the results I found that way did not match my case and I don't know where to look anymore.

Answer 1

You need to set options.EmitLegacyResourceAudienceClaim = true; when setting up the IdentityServer4, the default value is false.
It emits an aud claim with the format issuer/resources
Here is how ur code will look like:
namespace IdentityServer
{
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
var builder = services.AddIdentityServer(
options =>
{
options.EmitLegacyResourceAudienceClaim = true; //Default value is false
})
.AddInMemoryIdentityResources(Config.Ids)
.AddInMemoryApiResources(Config.Apis)
.AddInMemoryClients(Config.Clients)
.AddTestUsers(TestUsers.Users);
}
}
}
Read more about EmitLegacyResourceAudienceClaim here

Answer 2

Try to upgrade to version 4.0x of IdentityServer 4, think its back again in the latest release. Because I didn't see it in version 3.13 but I saw that it appeared in v4.0.0