About

Default ASP.NET Core Cors package does not allow to change CORS origins at runtime, this package allows to add custom implementation of CORS policy checking as a fallback when origin does not match any of the ones specified at startup. It can be used to retrieve origins from cache, database, file or to apply custom logic like allowing all when debug mode is on.

Installation

Use nuget to download the package.

Install-Package Mijalski.DynamicCorsPolicy

Usage

Firstly, create a class implementing interface IDynamicCorsPolicyResolver.

In Startup.ConfigureServices

replace: services.AddCors(); with services.AddDynamicCors<ExampleCorsPolicyResolver>(); and set policy name to: CorsPoliciesEnums.DynamicCorsPolicyName.

Lastly, in Startup.Configure

replace: app.UseCors(); with app.UseDynamicCorsMiddleware();.

Example

DynamicCorsPolicyResolver.cs:

public class DynamicCorsPolicyResolver : IDynamicCorsPolicyResolver
{

    private readonly ICorsCache _corsCache;

    public DynamicCorsPolicyResolver(ICorsCache corsCache)
    {
         _corsCache = corsCache;
    }

    public async Task<bool> ResolveForOrigin(string origin)
    {
        return await _corsCache.GetAsync(origin) != null;
    }
}

Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    // ...
    services.AddDynamicCors<DynamicCorsPolicyResolver>(options =>
    {
        options.AddPolicy(name: CorsPoliciesEnums.DynamicCorsPolicyName, builder =>
        {
            builder.WithOrigins("http://localhost:4200");
        });
     });
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
     // ...
     app.UseDynamicCorsMiddleware();
}

FAQ

Q: Will it be slower than regular CORS policy?

A: For origins specified at startup the speed will be the same, but for the external origins it will need to evaluate the custom logic written by you, as a part of ResolveForOrigin method.

Q: Is it based on ASP.NETCore CORS package?

A: Yes, it uses the same buildier and pipeline, but exposes an additional method to implement custom logic.

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

License

MIT