Add azuread provider

CHANGELOG.md

@@ -4,6 +4,7 @@ x.y.z (TBD)
 ### Breaking Changes
 
 ### Enhancements
+- Added Azure Active Directory (AzureAD) credentials provider. (#1254)
 
 ### Bug fixes
 

Platform.PCL/Realm.Sync.PCL/CredentialsPCL.cs

@@ -83,6 +83,17 @@ public static Credentials UsernamePassword(string username, string password, boo
             return null;
         }
 
+        /// <summary>
+        /// Creates <see cref="Credentials"/> based on a Facebook login.
+        /// </summary>
+        /// <param name="adToken">An access token, obtained by logging into Azure Active Directory.</param>
+        /// <returns>An instance of <see cref="Credentials"/> that can be used in <see cref="User.LoginAsync"/></returns>
+        public static Credentials AzureAD(string adToken)
+        {
+            RealmPCLHelpers.ThrowProxyShouldNeverBeUsed();
+            return null;
+        }
+
         /// <summary>
         /// Gets the identity provider for the credentials.
         /// </summary>

Shared/Realm.Sync.Shared/Credentials.cs

@@ -39,6 +39,8 @@ internal static class Providers
             internal const string Password = "password";
 
             internal const string AccessToken = "accessToken";
+
+            internal const string AzureAD = "azuread";
         }
 
         internal static class Keys
@@ -129,6 +131,21 @@ public static Credentials UsernamePassword(string username, string password, boo
             };
         }
 
+        /// <summary>
+        /// Creates <see cref="Credentials"/> based on a Facebook login.
+        /// </summary>
+        /// <param name="adToken">An access token, obtained by logging into Azure Active Directory.</param>
+        /// <returns>An instance of <see cref="Credentials"/> that can be used in <see cref="User.LoginAsync"/></returns>
+        public static Credentials AzureAD(string adToken)
+        {
+            if (adToken == null)
+            {
+                throw new ArgumentNullException(nameof(adToken));
+            }
+
+            return new Credentials { IdentityProvider = Providers.AzureAD, Token = adToken };
+        }
+
         internal static Credentials AccessToken(string accessToken, string identity, bool isAdmin = false)
         {
             return new Credentials