push notification relay service and relay send api

src/Core/Services/Implementations/BaseRelayPushNotificationService.cs

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+using System.Collections.Generic;
+using System.Threading.Tasks;
+using System.Net.Http;
+using Newtonsoft.Json;
+using System.Text;
+using System;
+using Newtonsoft.Json.Linq;
+using Bit.Core.Utilities;
+using System.Net;
+
+namespace Bit.Core.Services
+{
+    public abstract class BaseRelayPushNotificationService
+    {
+        private dynamic _decodedToken;
+        private DateTime? _nextAuthAttempt = null;
+
+        public BaseRelayPushNotificationService(
+            GlobalSettings globalSettings)
+        {
+            GlobalSettings = globalSettings;
+
+            PushClient = new HttpClient
+            {
+                BaseAddress = new Uri(globalSettings.PushRelayBaseUri)
+            };
+
+            IdentityClient = new HttpClient
+            {
+                BaseAddress = new Uri(globalSettings.Installation.IdentityUri)
+            };
+        }
+
+        protected HttpClient PushClient { get; private set; }
+        protected HttpClient IdentityClient { get; private set; }
+        protected GlobalSettings GlobalSettings { get; private set; }
+        protected string AccessToken { get; private set; }
+
+        protected async Task<bool> HandleTokenStateAsync()
+        {
+            if(_nextAuthAttempt.HasValue && DateTime.UtcNow > _nextAuthAttempt.Value)
+            {
+                return false;
+            }
+            _nextAuthAttempt = null;
+
+            if(!string.IsNullOrWhiteSpace(AccessToken) && !TokenExpired())
+            {
+                return true;
+            }
+
+            var requestMessage = new HttpRequestMessage
+            {
+                Method = HttpMethod.Post,
+                RequestUri = new Uri(IdentityClient.BaseAddress, "connect/token"),
+                Content = new FormUrlEncodedContent(new Dictionary<string, string>
+                {
+                    { "grant_type", "client_credentials" },
+                    { "scope", "api.push" },
+                    { "client_id", $"installation.{GlobalSettings.Installation.Id}" },
+                    { "client_secret", $"{GlobalSettings.Installation.Key}" }
+                })
+            };
+
+            var response = await IdentityClient.SendAsync(requestMessage);
+            if(!response.IsSuccessStatusCode)
+            {
+                if(response.StatusCode == HttpStatusCode.BadRequest)
+                {
+                    _nextAuthAttempt = DateTime.UtcNow.AddDays(1);
+                }
+
+                return false;
+            }
+
+            var responseContent = await response.Content.ReadAsStringAsync();
+            dynamic tokenResponse = JsonConvert.DeserializeObject(responseContent);
+            AccessToken = (string)tokenResponse.access_token;
+            return true;
+        }
+
+        protected class TokenHttpRequestMessage : HttpRequestMessage
+        {
+            public TokenHttpRequestMessage(string token)
+            {
+                Headers.Add("Authorization", $"Bearer {token}");
+            }
+
+            public TokenHttpRequestMessage(object requestObject, string token)
+                : this(token)
+            {
+                var stringContent = JsonConvert.SerializeObject(requestObject);
+                Content = new StringContent(stringContent, Encoding.UTF8, "application/json");
+            }
+        }
+
+        protected bool TokenExpired()
+        {
+            var decoded = DecodeToken();
+            var exp = decoded?["exp"];
+            if(exp == null)
+            {
+                throw new InvalidOperationException("No exp in token.");
+            }
+
+            var expiration = CoreHelpers.FromEpocMilliseconds(1000 * exp.Value<long>());
+            return DateTime.UtcNow < expiration;
+        }
+
+        protected JObject DecodeToken()
+        {
+            if(_decodedToken != null)
+            {
+                return _decodedToken;
+            }
+
+            if(AccessToken == null)
+            {
+                throw new InvalidOperationException($"{nameof(AccessToken)} not found.");
+            }
+
+            var parts = AccessToken.Split('.');
+            if(parts.Length != 3)
+            {
+                throw new InvalidOperationException($"{nameof(AccessToken)} must have 3 parts");
+            }
+
+            var decodedBytes = CoreHelpers.Base64UrlDecode(parts[1]);
+            if(decodedBytes == null || decodedBytes.Length < 1)
+            {
+                throw new InvalidOperationException($"{nameof(AccessToken)} must have 3 parts");
+            }
+
+            _decodedToken = JObject.Parse(Encoding.UTF8.GetString(decodedBytes, 0, decodedBytes.Length));
+            return _decodedToken;
+        }
+    }
+}