Create a custom cors policy to allow dynamic list of origins in Asp.Net

MyCorsPolicy.txt

[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = false)] 
public class MyCorsPolicy : Attribute, ICorsPolicyProvider 
{ 
    private CorsPolicy _policy; 
  
    public MyCorsPolicy() 
    { 
        // Create a CORS policy. 
        _policy = new CorsPolicy 
        { 
            AllowAnyMethod = true, 
            AllowAnyHeader = true
        }; 
  
        // Add allowed origins. 
        var origins = ConfigurationManager.AppSettings["CORSOrigin"].Split(','); 
  
        foreach (var origin in origins) 
        { 
            _policy.Origins.Add(origin); 
        } 
    } 
  
    public Task<CorsPolicy> GetCorsPolicyAsync(HttpRequestMessage request, CancellationToken cancellationToken) 
    { 
        return Task.FromResult(_policy); 
    } 
}