Add a recaptcha-script tag helper, which is responsible for adding a …

…script tag to load the recaptcha javascript api.

src/ReCaptcha/Enums/Render.cs

@@ -0,0 +1,12 @@
+namespace GSoftware.AspNetCore.ReCaptcha.TagHelpers
+{
+    /// <summary>
+    /// Rechaptcha rendering options for the <see cref="RecaptchaScriptTagHelper"/>.
+    /// </summary>
+    public enum Render
+    {
+        Explicit,
+        Onload,
+        V3
+    }
+}

src/ReCaptcha/ReCaptcha.csproj

@@ -22,6 +22,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.Mvc.Abstractions" Version="2.2.0" />
     <PackageReference Include="Microsoft.AspNetCore.Mvc.Core" Version="2.2.5" />
+    <PackageReference Include="Microsoft.AspNetCore.Razor" Version="2.2.0" />
     <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.9.6">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
@@ -47,8 +48,4 @@
     </EmbeddedResource>
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="TagHelpers\" />
-  </ItemGroup>
-
 </Project>

src/ReCaptcha/TagHelpers/RecaptchaScriptTagHelper.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Collections.Generic;
+using GSoftware.AspNetCore.ReCaptcha.Configuration;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.AspNetCore.WebUtilities;
+using Microsoft.Extensions.Options;
+
+namespace GSoftware.AspNetCore.ReCaptcha.TagHelpers
+{
+    /// <summary>
+    /// Adds a script tag, which will load the required reCAPTCHA JavaScript API. Can be added
+    /// anywhere on your HTML page, but if you use a onload callback function you must place this
+    /// after that callback to avoid race conditions.
+    /// </summary>
+    public class RecaptchaScriptTagHelper : TagHelper
+    {
+        private const string RecaptchaScriptEndpoint = "https://www.google.com/recaptcha/api.js";
+
+        private readonly RecaptchaSettings _settings;
+
+        public RecaptchaScriptTagHelper(IOptionsMonitor<RecaptchaSettings> settings)
+        {
+            _ = settings ?? throw new ArgumentNullException(nameof(settings));
+
+            _settings = settings.CurrentValue;
+        }
+
+        /// <summary>
+        /// Set the rendering mode for the script.
+        /// </summary>
+        public Render Render { get; set; } = Render.Onload;
+
+        /// <summary>
+        /// Set a callback function that will be called when reCAPTCHA has finished loading.
+        /// </summary>
+        public string? OnloadCallback { get; set; }
+
+        /// <summary>
+        /// Set a language code to force reCAPTCHA loading in the specified language. If not set language
+        /// will be detected automatically by reCAPTCHA. For a list of valid language codes visit: 
+        /// https://developers.google.com/recaptcha/docs/language
+        /// </summary>
+        public string? Language { get; set; }
+
+        /// <inheritdoc/>
+        public override void Process(TagHelperContext context, TagHelperOutput output)
+        {
+            _ = output ?? throw new ArgumentNullException(nameof(output));
+
+            output.TagName = "script";
+
+            if (Render == Render.V3)
+            {
+                output.Attributes.Add("src", $"{RecaptchaScriptEndpoint}?render={_settings.SiteKey}");
+            }
+            else
+            {
+                var queryCollection = new Dictionary<string, string>();
+
+                if (!string.IsNullOrEmpty(OnloadCallback))
+                {
+                    queryCollection.Add("onload", OnloadCallback);
+                }
+
+                if (Render == Render.Explicit)
+                {
+                    queryCollection.Add("render", Render.ToString().ToLowerInvariant());
+                }
+
+                if (!string.IsNullOrEmpty(Language))
+                {
+                    queryCollection.Add("hl", Language);
+                }
+
+                output.Attributes.Add("src", QueryHelpers.AddQueryString(RecaptchaScriptEndpoint, queryCollection));
+            }
+
+            output.Attributes.Add("async", null);
+            output.Attributes.Add("defer", null);
+        }
+    }
+}