Added snippet OAuth Token Manager

Snippets/Readme.md

@@ -0,0 +1,98 @@
+# Collection of Snippets
+
+## OAuth Token Manager
+
+Caches oauth tokens in a thread safe way
+
+```C#
+    class OAuthTokenManager
+    {
+        HttpClient httpClient = new HttpClient();
+
+        class AdquiredToken
+        {
+            internal string Token { get; set; }
+            internal DateTime ValidUntil { get; set; }
+
+            internal bool IsValid() => ValidUntil > DateTime.UtcNow;
+        }
+
+        private OAuthTokenManager()
+        {
+
+        }
+        static OAuthTokenManager singleton = new OAuthTokenManager();
+
+
+        static internal OAuthTokenManager Instance { get { return singleton; } }
+
+
+        Dictionary<string, AdquiredToken> adquiredTokens = new Dictionary<string, AdquiredToken>();
+        SemaphoreSlim semaphoreSlim = new SemaphoreSlim(1, 1);
+
+        internal async Task<string> GetToken(string uri, string grantType, string clientId, string clientSecret, TimeSpan validity)
+        {
+            if (adquiredTokens.TryGetValue(uri, out var adquiredToken))
+            {
+                if (adquiredToken.IsValid())
+                    return adquiredToken.Token;
+            }
+
+            await semaphoreSlim.WaitAsync();
+            try
+            {
+                if (adquiredTokens.TryGetValue(uri, out adquiredToken))
+                {
+                    if (adquiredToken.IsValid())
+                    {
+                        return adquiredToken.Token;
+                    }
+                }
+
+                adquiredToken = await ObtainToken(uri, grantType, clientId, clientSecret, validity);
+                if (adquiredToken != null)
+                {
+                    adquiredTokens[uri] = adquiredToken;
+                    return adquiredToken.Token;
+                }
+                else
+                {
+                    adquiredTokens.Remove(uri);
+                }
+            }
+            finally
+            {
+                semaphoreSlim.Release();
+            }
+
+            return null;
+        }
+
+        private async Task<AdquiredToken> ObtainToken(string uri, string grantType, string clientId, string clientSecret, TimeSpan validity)
+        {
+            // 1. Get auth token
+            var formContent = new FormUrlEncodedContent(new[]
+            {
+                new KeyValuePair<string, string>("grant_type", grantType),
+                new KeyValuePair<string, string>("client_id", clientId),
+                new KeyValuePair<string, string>("client_secret", clientSecret),
+
+            });
+            var tokenRes = await httpClient.PostAsync(uri, formContent);
+
+            if (tokenRes.IsSuccessStatusCode)
+            {
+                var authResPayload = JsonConvert.DeserializeObject<JToken>(await tokenRes.Content.ReadAsStringAsync());
+                var token = authResPayload["access_token"].ToString();
+                return new AdquiredToken
+                {
+                    Token = token,
+                    ValidUntil = DateTime.UtcNow.Add(validity)
+                };
+            }
+
+            return null;
+        }
+    }
+
+```