Wildcard Origin Cors Policy

WildcardOriginCorsPolicy.cs

public class WildcardOriginCorsPolicy : Attribute, ICorsPolicyProvider
    {
        private readonly string _origins;
        private readonly string _headers;
        private readonly string _methods;

        //private readonly CorsPolicy _policy;
        //
        // Summary:
        //     Initializes a new instance of the WildcardOriginCorsPolicy class.
        //
        // Parameters:
        //   origins:
        //     Comma-separated list of origins that are allowed to access the resource. Use
        //     "*" to allow all.
        //     "*.example.com" for subdomains
        //
        //   headers:
        //     Comma-separated list of headers that are supported by the resource. Use "*" to
        //     allow all. Use null or empty string to allow none.
        //
        //   methods:
        //     Comma-separated list of methods that are supported by the resource. Use "*" to
        //     allow all. Use null or empty string to allow none.
        public WildcardOriginCorsPolicy(string origins, string headers, string methods)
        {
            this._origins = origins;
            this._headers = headers;
            this._methods = methods;
        }

        public bool SupportsCredentials { get; set; }

        public Task<CorsPolicy> GetCorsPolicyAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            var policy = CreatePolicy(request.GetCorsRequestContext(), this._origins, this._headers, this._methods);
            policy.SupportsCredentials = this.SupportsCredentials;

            return Task.FromResult(policy);
        }

        private static CorsPolicy CreatePolicy(CorsRequestContext requestContext, string origins, string headers, string methods)
        {

            var corsPolicy = new CorsPolicy();
            if (origins == "*")
            {
                corsPolicy.AllowAnyOrigin = true;
            }
            else
            {
                var originsStringArray = origins.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                var requestOrigin = requestContext.Origin.ToLowerInvariant();

                foreach (var originItem in originsStringArray)
                {
                    ////Check if the current request uri matches with any of the wildcard origins.
                    if (Regex.IsMatch(requestOrigin, WildCardToRegularExpression(originItem)))
                    {
                        corsPolicy.Origins.Add(requestOrigin);
                    }
                }
            }

            if (!String.IsNullOrEmpty(headers))
            {
                if (headers == "*")
                {
                    corsPolicy.AllowAnyHeader = true;
                }
                else
                {
                    var headersStringArray = headers.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                    corsPolicy.Headers.AddAll(headersStringArray);
                }
            }

            if (!String.IsNullOrEmpty(methods))
            {
                if (methods == "*")
                {
                    corsPolicy.AllowAnyMethod = true;
                }
                else
                {
                    var methodsStringArray = methods.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                    corsPolicy.Methods.AddAll(methodsStringArray);
                }
            }

            return corsPolicy;
        }

        private static string WildCardToRegularExpression(String value)
        {
            return "^" + Regex.Escape(value).Replace("\\?", ".").Replace("\\*", ".*") + "$";
        }
    }

AddAll came from one of my extensions. You can replace it with custom code.