Global Resource Authorization based on route value

user_1121245 0
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I'm working on an ASP.Net Core 3.1 web API.

The API users are from an Azure AD. The users can access the API if they have a license, each user can be assigned to multiple licenses and the same license can be assigned to multiple users.

The client want me to structure the API routes with a template like <api_url>/{licenseId}/controller/action.

My controllers are like:

[Authorize]
[Route("{licenseId}/Foo")]
public class FooController : ControllerBase
{

If I think of the License as a Resource, I can use the Resource based authorization as detailed here. It works but I find myself copying and pasting the auth check for all the actions.

Is there a better way to authorize an user using the route values?

Here what I've got so far:

public class LicenseRequirement : IAuthorizationRequirement
{        
    public Guid LicenseId { get; private set; }

    public LicenseRequirement(Guid licenseId)
    {
        LicenseId = licenseId;
    }
}

public class LicenseAuthorizationHandler : AuthorizationHandler<LicenseRequirement>
{
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly ILogger<LicenseAuthorizationHandler> _logger;
    private readonly DBContext _db;

    public LicenseAuthorizationHandler(DBContext context, ILogger<LicenseAuthorizationHandler> logger, IHttpContextAccessor httpContextAccessor)
    {
        _logger = logger;
        _db = context;
        _httpContextAccessor = httpContextAccessor;
    }

    protected override async Task HandleRequirementAsync(AuthorizationHandlerContext context, LicenseRequirement requirement)
    {
        var userId = new Guid(context.User.GetUserId());
        var licenseId = _httpContextAccessor.HttpContext.GetRouteData().Values["licenseId"];

        if (await _db.ApiUsers.SingleOrDefaultAsync(x => x.LicenseId == new Guid(licenseId as string) && x.UserId == userId) is ApiUser user)
            context.Succeed(requirement);
    }
}

Now I'm a bit stuck as I don't know how to set it up in Startup.cs and use it as an attribute or area filter creating those requirement at runtime with the licenseId route's value.

asp.net-authorization asp.net-core asp.net-core-webapi routes c#
1 Answers

I found IAuthorizationFilter pretty straightforward to implement. When I tried it yesterday, I couldn't found the RouteValues but they're there:

public class LicenseAuthorizationFilter : IAuthorizationFilter
{
    private readonly ILogger<LicenseAuthorizationFilter> _logger;
    private readonly DBContext _db;

    public LicenseAuthorizationFilter(DBContext context, ILogger<LicenseAuthorizationFilter> logger)
    {
        _logger = logger;
        _db = context;
    }

    public void OnAuthorization(AuthorizationFilterContext context)
    {
        var userId = new Guid(context.HttpContext.User.GetUserId());
        var licenseId = new Guid(context.HttpContext.Request.RouteValues["licenseId"] as string);

        if (!(_db.ApiUsers.SingleOrDefault(x => x.LicenseId == licenseId && x.UserId == userId) is ApiUser user))
        {
            context.Result = new ForbidResult();
        }
    }
}

public class LicenseAuthorizationAttribute : TypeFilterAttribute
{
    public LicenseAuthorizationAttribute() : base(typeof(LicenseAuthorizationFilter))
    { }
}

And the controller can neatly become:

[Authorize]
[LicenseAuthorization]
[Route("{licenseId}/Items")]
public class ItemsController : ControllerBase
{
    [...]
}
user_11212450
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