public interface IAuthorizationProvider

Public Interface IAuthorizationProvider

public interface class IAuthorizationProvider

type IAuthorizationProvider =  interface end

/// <summary>
/// Cognitive Services Authorization Provider.
/// </summary>
public sealed class CognitiveServicesAuthorizationProvider : IAuthorizationProvider
{
    /// <summary>
    /// The fetch token URI
    /// </summary>
    private const string FetchTokenUri = "https://api.cognitive.microsoft.com/sts/v1.0";

    /// <summary>
    /// The subscription key
    /// </summary>
    private readonly string subscriptionKey;

    /// <summary>
    /// Initializes a new instance of the <see cref="CognitiveServicesAuthorizationProvider" /> class.
    /// </summary>
    /// <param name="subscriptionKey">The subscription identifier.</param>
    public CognitiveServicesAuthorizationProvider(string subscriptionKey)
    {
        if (subscriptionKey == null)
        {
            throw new ArgumentNullException(nameof(subscriptionKey));
        }

        if (string.IsNullOrWhiteSpace(subscriptionKey))
        {
            throw new ArgumentException(nameof(subscriptionKey));
        }

        this.subscriptionKey = subscriptionKey;
    }

    /// <summary>
    /// Gets the authorization token asynchronously.
    /// </summary>
    /// <returns>
    /// A task that represents the asynchronous read operation. The value of the string parameter contains the next the authorization token.
    /// </returns>
    /// <remarks>
    /// This method should always return a valid authorization token at the time it is called.
    /// </remarks>
    public Task<string> GetAuthorizationTokenAsync()
    {
        // Use token caching instead of returning a new token every time this is called.
        return FetchToken(FetchTokenUri, this.subscriptionKey);
    }

    /// <summary>
    /// Fetches the token.
    /// </summary>
    /// <param name="fetchUri">The fetch URI.</param>
    /// <param name="subscriptionKey">The subscription key.</param>
    /// <returns>An access token.</returns>
    private static async Task<string> FetchToken(string fetchUri, string subscriptionKey)
    {
        using (var client = new HttpClient())
        {
            client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", subscriptionKey);
            var uriBuilder = new UriBuilder(fetchUri);
            uriBuilder.Path += "/issueToken";

            using (var result = await client.PostAsync(uriBuilder.Uri.AbsoluteUri, null).ConfigureAwait(false))
            {
                return await result.Content.ReadAsStringAsync().ConfigureAwait(false);
            }
        }
    }
}