Configure cors to allow all subdomains using ASP.NET Core (Asp.net 5, MVC6, VNext)
Solution 1:
This has now been implemented in version 2.0.0. In your ConfigureServices use the following:
options.AddPolicy("MyCorsPolicy",
builder => builder
.SetIsOriginAllowedToAllowWildcardSubdomains()
.WithOrigins("https://*.mydomain.com")
.AllowAnyMethod()
.AllowCredentials()
.AllowAnyHeader()
.Build()
);
Also, don't forget to call UseCors in your Configure call too:
app.UseCors("MyCorsPolicy");
Solution 2:
I submitted a pull request to the ASP.NET team with this change so hopefully it will make it into the nuget package. Until then, I use this workaround.
Below you register cors as usual with the exception of having to register the WildCardCorsService class in the di container.
public virtual IServiceProvider ConfigureServices(IServiceCollection services)
{
services.TryAdd(ServiceDescriptor.Transient<ICorsService, WildCardCorsService>());
services.AddCors
(
options =>
{
options.AddPolicy
(
CORSDefaults.PolicyName,
builder =>
{
builder
.WithOrigins("http://*.withwildcardsubdomain.com", "http://nowildcard.com")
.AllowAnyHeader()
.AllowAnyMethod()
.AllowCredentials();
}
);
}
);
}
Save this class locally in your solution. It is a copy and edit of the Microsoft.AspNet.Cors.CorsService.cs class to allow it to handle wildcard subdomains. If it finds a wildcard char '*' it will check if the root domain matches on allowed origins and actual origin. It does NOT support partial wildcard matching.
namespace Microsoft.AspNet.Cors.Infrastructure
{
/// <summary>
/// This ICorsService should be used in place of the official default CorsService to support origins
/// like http://*.example.comwhich will allow any subdomain for example.com
/// </summary>
public class WildCardCorsService : ICorsService
{
private readonly CorsOptions _options;
/// <summary>
/// Creates a new instance of the <see cref="CorsService"/>.
/// </summary>
/// <param name="options">The option model representing <see cref="CorsOptions"/>.</param>
public WildCardCorsService(IOptions<CorsOptions> options)
{
if (options == null)
{
throw new ArgumentNullException(nameof(options));
}
_options = options.Value;
}
/// <summary>
/// Looks up a policy using the <paramref name="policyName"/> and then evaluates the policy using the passed in
/// <paramref name="context"/>.
/// </summary>
/// <param name="requestContext"></param>
/// <param name="policyName"></param>
/// <returns>A <see cref="CorsResult"/> which contains the result of policy evaluation and can be
/// used by the caller to set appropriate response headers.</returns>
public CorsResult EvaluatePolicy(HttpContext context, string policyName)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
var policy = _options.GetPolicy(policyName);
return EvaluatePolicy(context, policy);
}
/// <inheritdoc />
public CorsResult EvaluatePolicy(HttpContext context, CorsPolicy policy)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (policy == null)
{
throw new ArgumentNullException(nameof(policy));
}
var corsResult = new CorsResult();
var accessControlRequestMethod = context.Request.Headers[Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlRequestMethod];
if (string.Equals(context.Request.Method, Microsoft.AspNet.Cors.Infrastructure.CorsConstants.PreflightHttpMethod, StringComparison.Ordinal) &&
!StringValues.IsNullOrEmpty(accessControlRequestMethod))
{
EvaluatePreflightRequest(context, policy, corsResult);
}
else
{
EvaluateRequest(context, policy, corsResult);
}
return corsResult;
}
public virtual void EvaluateRequest(HttpContext context, CorsPolicy policy, CorsResult result)
{
var origin = context.Request.Headers[Microsoft.AspNet.Cors.Infrastructure.CorsConstants.Origin];
if (!OriginIsAllowed(origin, policy))
{
return;
}
AddOriginToResult(origin, policy, result);
result.SupportsCredentials = policy.SupportsCredentials;
AddHeaderValues(result.AllowedExposedHeaders, policy.ExposedHeaders);
}
public virtual void EvaluatePreflightRequest(HttpContext context, CorsPolicy policy, CorsResult result)
{
var origin = context.Request.Headers[Microsoft.AspNet.Cors.Infrastructure.CorsConstants.Origin];
if (!OriginIsAllowed(origin, policy))
{
return;
}
var accessControlRequestMethod = context.Request.Headers[Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlRequestMethod];
if (StringValues.IsNullOrEmpty(accessControlRequestMethod))
{
return;
}
var requestHeaders =
context.Request.Headers.GetCommaSeparatedValues(Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlRequestHeaders);
if (!policy.AllowAnyMethod && !policy.Methods.Contains(accessControlRequestMethod))
{
return;
}
if (!policy.AllowAnyHeader &&
requestHeaders != null &&
!requestHeaders.All(header => Microsoft.AspNet.Cors.Infrastructure.CorsConstants.SimpleRequestHeaders.Contains(header, StringComparer.OrdinalIgnoreCase) ||
policy.Headers.Contains(header, StringComparer.OrdinalIgnoreCase)))
{
return;
}
AddOriginToResult(origin, policy, result);
result.SupportsCredentials = policy.SupportsCredentials;
result.PreflightMaxAge = policy.PreflightMaxAge;
result.AllowedMethods.Add(accessControlRequestMethod);
AddHeaderValues(result.AllowedHeaders, requestHeaders);
}
/// <inheritdoc />
public virtual void ApplyResult(CorsResult result, HttpResponse response)
{
if (result == null)
{
throw new ArgumentNullException(nameof(result));
}
if (response == null)
{
throw new ArgumentNullException(nameof(response));
}
var headers = response.Headers;
if (result.AllowedOrigin != null)
{
headers[Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlAllowOrigin] = result.AllowedOrigin;
}
if (result.VaryByOrigin)
{
headers["Vary"] = "Origin";
}
if (result.SupportsCredentials)
{
headers[Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlAllowCredentials] = "true";
}
if (result.AllowedMethods.Count > 0)
{
// Filter out simple methods
var nonSimpleAllowMethods = result.AllowedMethods
.Where(m =>
!Microsoft.AspNet.Cors.Infrastructure.CorsConstants.SimpleMethods.Contains(m, StringComparer.OrdinalIgnoreCase))
.ToArray();
if (nonSimpleAllowMethods.Length > 0)
{
headers.SetCommaSeparatedValues(
Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlAllowMethods,
nonSimpleAllowMethods);
}
}
if (result.AllowedHeaders.Count > 0)
{
// Filter out simple request headers
var nonSimpleAllowRequestHeaders = result.AllowedHeaders
.Where(header =>
!Microsoft.AspNet.Cors.Infrastructure.CorsConstants.SimpleRequestHeaders.Contains(header, StringComparer.OrdinalIgnoreCase))
.ToArray();
if (nonSimpleAllowRequestHeaders.Length > 0)
{
headers.SetCommaSeparatedValues(
Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlAllowHeaders,
nonSimpleAllowRequestHeaders);
}
}
if (result.AllowedExposedHeaders.Count > 0)
{
// Filter out simple response headers
var nonSimpleAllowResponseHeaders = result.AllowedExposedHeaders
.Where(header =>
!Microsoft.AspNet.Cors.Infrastructure.CorsConstants.SimpleResponseHeaders.Contains(header, StringComparer.OrdinalIgnoreCase))
.ToArray();
if (nonSimpleAllowResponseHeaders.Length > 0)
{
headers.SetCommaSeparatedValues(
Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlExposeHeaders,
nonSimpleAllowResponseHeaders);
}
}
if (result.PreflightMaxAge.HasValue)
{
headers[Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AccessControlMaxAge]
= result.PreflightMaxAge.Value.TotalSeconds.ToString(CultureInfo.InvariantCulture);
}
}
protected virtual bool OriginIsAllowed(string origin, CorsPolicy policy)
{
if (!string.IsNullOrWhiteSpace(origin) &&
(policy.AllowAnyOrigin ||
policy.Origins.Contains(origin) ||
IsWildCardSubdomainMatch(origin, policy)))
return true;
return false;
}
private void AddOriginToResult(string origin, CorsPolicy policy, CorsResult result)
{
if (policy.AllowAnyOrigin)
{
if (policy.SupportsCredentials)
{
result.AllowedOrigin = origin;
result.VaryByOrigin = true;
}
else
{
result.AllowedOrigin = Microsoft.AspNet.Cors.Infrastructure.CorsConstants.AnyOrigin;
}
}
else
{
result.AllowedOrigin = origin;
}
}
private static void AddHeaderValues(IList<string> target, IEnumerable<string> headerValues)
{
if (headerValues == null)
{
return;
}
foreach (var current in headerValues)
{
target.Add(current);
}
}
private bool IsWildCardSubdomainMatch(string origin, CorsPolicy policy)
{
var actualOriginUri = new Uri(origin);
var actualOriginRootDomain = GetRootDomain(actualOriginUri);
foreach (var o in policy.Origins)
{
if (!o.Contains("*"))
continue;
// 1) CANNOT USE System.Text.RegularExpression since it does not exist in .net platform 5.4 (which the Microsoft.AspNet.Cors project.json targets)
// 2) '*' char is not valid for creation of a URI object so we replace it just for this comparison
var allowedOriginUri = new Uri(o.Replace("*", "SOMELETTERS"));
if (allowedOriginUri.Scheme == actualOriginUri.Scheme &&
actualOriginRootDomain == GetRootDomain(allowedOriginUri))
return true;
}
return false;
}
private string GetRootDomain(Uri uri)
{
//Got this snippet here http://stackoverflow.com/questions/16473838/get-domain-name-of-a-url-in-c-sharp-net
var host = uri.Host;
int index = host.LastIndexOf('.'), last = 3;
while (index > 0 && index >= last - 3)
{
last = index;
index = host.LastIndexOf('.', last - 1);
}
return host.Substring(index + 1);
}
}
/// <summary>
/// Needed to copy these in since some of them are internal to the Microsoft.AspNet.Cors project
/// </summary>
public static class CorsConstants
{
/// <summary>The HTTP method for the CORS preflight request.</summary>
public static readonly string PreflightHttpMethod = "OPTIONS";
/// <summary>The Origin request header.</summary>
public static readonly string Origin = "Origin";
/// <summary>
/// The value for the Access-Control-Allow-Origin response header to allow all origins.
/// </summary>
public static readonly string AnyOrigin = "*";
/// <summary>The Access-Control-Request-Method request header.</summary>
public static readonly string AccessControlRequestMethod = "Access-Control-Request-Method";
/// <summary>The Access-Control-Request-Headers request header.</summary>
public static readonly string AccessControlRequestHeaders = "Access-Control-Request-Headers";
/// <summary>The Access-Control-Allow-Origin response header.</summary>
public static readonly string AccessControlAllowOrigin = "Access-Control-Allow-Origin";
/// <summary>The Access-Control-Allow-Headers response header.</summary>
public static readonly string AccessControlAllowHeaders = "Access-Control-Allow-Headers";
/// <summary>The Access-Control-Expose-Headers response header.</summary>
public static readonly string AccessControlExposeHeaders = "Access-Control-Expose-Headers";
/// <summary>The Access-Control-Allow-Methods response header.</summary>
public static readonly string AccessControlAllowMethods = "Access-Control-Allow-Methods";
/// <summary>The Access-Control-Allow-Credentials response header.</summary>
public static readonly string AccessControlAllowCredentials = "Access-Control-Allow-Credentials";
/// <summary>The Access-Control-Max-Age response header.</summary>
public static readonly string AccessControlMaxAge = "Access-Control-Max-Age";
internal static readonly string[] SimpleRequestHeaders = new string[4]
{
"Origin",
"Accept",
"Accept-Language",
"Content-Language"
};
internal static readonly string[] SimpleResponseHeaders = new string[6]
{
"Cache-Control",
"Content-Language",
"Content-Type",
"Expires",
"Last-Modified",
"Pragma"
};
internal static readonly string[] SimpleMethods = new string[3]
{
"GET",
"HEAD",
"POST"
};
}
}
Enjoy!