Defining the Authority - identityserver4

Question

Currently I'm doing the following
services.AddAuthentication("Bearer")
.AddIdentityServerAuthentication(options =>
{
options.Authority = Configuration.GetValue<string>("IdentityServer:Authority");
options.RequireHttpsMetadata = Configuration.GetValue<bool>("IdentityServer:RequireHttps");
options.ApiName = Configuration.GetValue<string>("IdentityServer:UserManagementApi:ResourceName");
options.SaveToken = true;
})
.AddCookie(cfg => cfg.SlidingExpiration = true);
Where I'm getting the Authority from the config file. However, we are upgrading our app to be multi-tenant and need to set these values depending on the tenant being called. Is it possible to set these values from a service that will find the tenant at runtime using IOC.
We are using Dotnet Code 2.2 and Lamar IOC.
There is what appears to be a duplicate of this, however, I have the following issue as we are running a number of microservices.
Each Tenant has it's own IdentityServer4 tenant, that uses it's own database. This is a standalone service to manage the users.
Each Api uses it's own tenanted IdentityServer api to authenticate.
So
Api Site ----> connects to IdentityServer4 Site
eg.
api1.company1.com connects to auth.company1.com to authenticate
api2.company1.com connects to auth.company1.com to authenticate
api1.company2.com connects to auth.company2.com to authenticate
api2.company2.com connects to auth.company2.com to authenticate
Each Api will call other api's and pass the user token on to authenticate. I need a way to tell the api what auth to use to authenticate. Using a shared Authority, when getting the token you get the following
{
"nbf": 1556619889,
"exp": 1556623489,
"iss": "http://shared-domain-for-every-tenant,
"aud": [
"http://shared-domain-for-every-tenant/resources",
"api1",
"api2"
],
"client_id": "postman",
"scope": [
"api1",
"api1"
]
}