How to combine the REST API from Azure API Management with LINQ and a Subscription key to get the UserId

Enable access to the REST API

Read the subscription key value from the request header

Modify the methods in the Web API Controller class to read the "Ocp-Apim-Subscription-Key" value from the request header. Return a HTTP 401 Unauthorized error if the value is not present.

IEnumerable<string> headerValues;
string subscriptionKey = null;

if (Request.Headers.TryGetValues("Ocp-Apim-Subscription-Key", out headerValues))
{
     subscriptionKey = headerValues.FirstOrDefault();
}

Create a Repository class to get the UserId

In the Web API Controller class call the Repository class to get the user id with the "Ocp-Apim-Subscription-Key" as a input parameter. In the Repository call the GET Subscriptions operation from the API Management REST API to return a collection of all subscriptions. Then you can use a LINQ query on the result subscriptions list to get the subscription from the user.

public class ApimRepository
{

    string ApimRestHost = ConfigurationManager.AppSettings["ApimRestHost"];
    string ApimRestAuthHeader = ConfigurationManager.AppSettings
    ["ApimRestAuthHeader"];
    string ApimRestApiVersion = "2014-02-14-preview";      

    public async Task<string> GetUserIdByToken(string primaryKey)
    {

        string userId = null;

        using (var client = new HttpClient())
        {

            client.BaseAddress = new Uri(ApimRestHost);
             client.DefaultRequestHeaders.Add("Authorization",    
                                         ApimRestAuthHeader);

            // Get all the subscriptions from API Management
            HttpResponseMessage response = await client.GetAsync
            ("/subscriptions?api-version=" + ApimRestApiVersion);
            if (response.IsSuccessStatusCode)
             {
                HttpContent cont = response.Content;        

                string jsonContent = cont.ReadAsStringAsync().Result;
                Subscriptions list = JsonConvert.DeserializeObject
                                     <Subscriptions>(jsonContent);

                // Get the specific subscription from the list with LINQ
                Subscription s = list.value.Where(a => a.primaryKey == 
                                            primaryKey).FirstOrDefault();

                if (s != null)
                {
                     // Remove "/users/" from id
                    userId = s.userId.Substring(7);
                }
            }
         }

        return userId;
    }
}

Wrap Up

The REST Web API from Azure API Management makes it very easy to get information on selected entities, such as users, groups, products, and subscriptions. Combining it with LINQ adds even more functionality because now you have extra properties where you can filter on!

You can download the code here:
Console-App-that-combines-the-Azure-API-Management-REST-API-with-LINQ