firebase
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # Unreleased
 
+- [added] `WebpushFcmOptions` added to the `WebpushConfig` class.
 - [added] Implemented the `GetUserByEmailAsync()` and `GetUserByPhoneNumberAsync()`
   APIs in the `FirebaseAuth` class.
 

diff --git a/FirebaseAdmin/FirebaseAdmin.Tests/Messaging/MessageTest.cs b/FirebaseAdmin/FirebaseAdmin.Tests/Messaging/MessageTest.cs
@@ -1558,6 +1558,98 @@ public void ApnsInvalidCriticalSoundVolumeTooHigh()
             Assert.Throws<ArgumentException>(() => message.CopyAndValidate());
         }
 
+        [Fact]
+        public void WebpushNotificationWithLinkUrl()
+        {
+            var message = new Message()
+            {
+                Topic = "test-topic",
+                Webpush = new WebpushConfig()
+                {
+                    Notification = new WebpushNotification()
+                    {
+                        Title = "title",
+                        Body = "body",
+                        Icon = "icon",
+                    },
+                    FcmOptions = new WebpushFcmOptions()
+                    {
+                        Link = "https://www.firebase.io/",
+                    },
+                },
+            };
+            var expected = new JObject()
+            {
+                { "topic", "test-topic" },
+                {
+                    "webpush", new JObject()
+                    {
+                        {
+                            "notification", new JObject()
+                            {
+                                { "title", "title" },
+                                { "body", "body" },
+                                { "icon", "icon" },
+                            }
+                        },
+                        {
+                            "fcm_options", new JObject()
+                            {
+                                { "link", "https://www.firebase.io/" },
+                            }
+                        },
+                    }
+                },
+            };
+            this.AssertJsonEquals(expected, message);
+        }
+
+        [Fact]
+        public void WebpushNotificationWithInvalidHttpLinkUrl()
+        {
+            var message = new Message()
+            {
+                Topic = "test-topic",
+                Webpush = new WebpushConfig()
+                {
+                    Notification = new WebpushNotification()
+                    {
+                        Title = "title",
+                        Body = "body",
+                        Icon = "icon",
+                    },
+                    FcmOptions = new WebpushFcmOptions()
+                    {
+                        Link = "http://www.firebase.io/",
+                    },
+                },
+            };
+            Assert.Throws<ArgumentException>(() => message.CopyAndValidate());
+        }
+
+        [Fact]
+        public void WebpushNotificationWithInvalidHttpsLinkUrl()
+        {
+            var message = new Message()
+            {
+                Topic = "test-topic",
+                Webpush = new WebpushConfig()
+                {
+                    Notification = new WebpushNotification()
+                    {
+                        Title = "title",
+                        Body = "body",
+                        Icon = "icon",
+                    },
+                    FcmOptions = new WebpushFcmOptions()
+                    {
+                        Link = "https whatever",
+                    },
+                },
+            };
+            Assert.Throws<ArgumentException>(() => message.CopyAndValidate());
+        }
+
         private void AssertJsonEquals(JObject expected, Message actual)
         {
             var json = NewtonsoftJsonSerializer.Instance.Serialize(actual.CopyAndValidate());

diff --git a/FirebaseAdmin/FirebaseAdmin/Messaging/WebpushConfig.cs b/FirebaseAdmin/FirebaseAdmin/Messaging/WebpushConfig.cs
@@ -44,6 +44,12 @@ public sealed class WebpushConfig
         [JsonProperty("notification")]
         public WebpushNotification Notification { get; set; }
 
+        /// <summary>
+        /// Gets or sets the Webpush options that will be included in the message.
+        /// </summary>
+        [JsonProperty("fcm_options")]
+        public WebpushFcmOptions FcmOptions { get; set; }
+
         /// <summary>
         /// Copies this Webpush config, and validates the content of it to ensure that it can be
         /// serialized into the JSON format expected by the FCM service.
@@ -55,6 +61,7 @@ internal WebpushConfig CopyAndValidate()
                 Headers = this.Headers?.Copy(),
                 Data = this.Data?.Copy(),
                 Notification = this.Notification?.CopyAndValidate(),
+                FcmOptions = this.FcmOptions?.CopyAndValidate(),
             };
         }
     }

diff --git a/FirebaseAdmin/FirebaseAdmin/Messaging/WebpushFcmOptions.cs b/FirebaseAdmin/FirebaseAdmin/Messaging/WebpushFcmOptions.cs
@@ -0,0 +1,54 @@
+// Copyright 2019, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System;
+using Newtonsoft.Json;
+
+namespace FirebaseAdmin.Messaging
+{
+    /// <summary>
+    /// Represents the Webpush-specific notification options that can be included in a <see cref="Message"/>.
+    /// See <see href="https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages#WebpushFcmOptions">this link</see>.
+    /// </summary>
+    public sealed class WebpushFcmOptions
+    {
+        /// <summary>
+        /// Gets or sets the link to open when the user clicks on the notification. For all URL values, HTTPS is required.
+        /// </summary>
+        [JsonProperty("link")]
+        public string Link { get; set; }
+
+        /// <summary>
+        /// Copies this Webpush FCM options, and validates the content of it to ensure that it can
+        /// be serialized into the JSON format expected by the FCM service.
+        /// </summary>
+        internal WebpushFcmOptions CopyAndValidate()
+        {
+            var copy = new WebpushFcmOptions()
+            {
+                Link = this.Link,
+            };
+
+            if (copy.Link != null)
+            {
+                if (!Uri.IsWellFormedUriString(copy.Link, UriKind.Absolute) || !copy.Link.StartsWith("https"))
+                {
+                    throw new ArgumentException("The link options should be a valid https url.");
+                }
+            }
+
+            return copy;
+        }
+    }
+}