TokenValidationHandler

TokenValidationHandler.cs

public class TokenValidationHandler : DelegatingHandler
{
    private readonly string _storageConnectionString = CloudConfigurationManager.GetSetting("StorageConnectionString");

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        const string errorMessage = "Unauthorized access; {0}";
        const HttpStatusCode code = HttpStatusCode.Unauthorized;
            
        var authValue = request.Headers.Authorization;

        if (authValue == null)
            return CreateErrorResponse(string.Format(errorMessage, "requires authorization header"), code);

        if (String.IsNullOrWhiteSpace(authValue.Scheme))
            return CreateErrorResponse(string.Format(errorMessage, "requires authorization scheme and parameter"), code);
            
        if (authValue.Scheme != "Auth")
            return CreateErrorResponse(string.Format(errorMessage, "invalid authorization scheme"), code);

        if (String.IsNullOrWhiteSpace(authValue.Parameter))
            return CreateErrorResponse(string.Format(errorMessage, "missing authorization parameter"), code);

        var serverKey = authValue.Parameter;

        var table = Storage.GetStorageTable(_storageConnectionString, "serverkey");
        var query = new TableQuery<ServerKeyEntity>().Where(
            TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, serverKey));
        var serverKeyEntity = table.ExecuteQuery(query).FirstOrDefault();

        if (serverKeyEntity == null)
            return CreateErrorResponse(string.Format(errorMessage, "invalid key"), code);

        var userId = serverKeyEntity.RowKey;
        request.Headers.Add("UserId", userId);
        
        var response = await base.SendAsync(request, cancellationToken);
        return response;
    }

    private static HttpResponseMessage CreateErrorResponse(string errorMessage, HttpStatusCode httpStatusCode)
    {
        return new HttpResponseMessage(httpStatusCode)
        {
            Content = new StringContent(errorMessage)
        };
    }
}