Created a token provider using options monitor.

src/Weatherstack/Security/OptionsTokenProvider.cs

@@ -0,0 +1,82 @@
+// Copyright (c) 2024 tacosontitan
+// This file is part of the Weatherstack project, which is distributed under the MIT license.
+// See LICENSE for more information.
+
+using Microsoft.Extensions.Options;
+
+namespace Weatherstack.Security;
+
+/// <summary>
+///     Represents a token provider that returns a token from an
+///     <see cref="IOptionsMonitor{T}"/> instance.
+/// </summary>
+public sealed class OptionsTokenProvider
+    : ITokenProvider
+{
+    private string? _token;
+
+    /// <summary>
+    ///     Creates a new <see cref="ITokenProvider"/> instance focused
+    ///     on the token provided by the specified <paramref name="options"/>.
+    /// </summary>
+    /// <param name="options">
+    ///     The options to use for the token.
+    /// </param>
+    public OptionsTokenProvider(IOptionsMonitor<WeatherstackOptions> options)
+    {
+        #if NET6_0_OR_GREATER
+
+        ArgumentNullException.ThrowIfNull(options);
+
+        #else
+
+        if (options is null)
+            throw new ArgumentNullException(nameof(options));
+
+        #endif
+
+        _token = options.CurrentValue.Token;
+        options.OnChange(UpdateToken);
+
+        void UpdateToken(WeatherstackOptions options) =>
+            _token = options.Token;
+    }
+
+    /// <inheritdoc />
+    /// <exception cref="ArgumentNullException">
+    ///     Thrown when the token is <see langword="null"/>.
+    /// </exception>
+    /// <exception cref="ArgumentException">
+    ///     Thrown when the token is empty or whitespace.
+    /// </exception>
+    public string GetToken()
+    {
+        ValidateToken(_token);
+        return _token!;
+    }
+
+    private static void ValidateToken(string? token)
+    {
+        #if NET6_0_OR_GREATER
+
+        ArgumentNullException.ThrowIfNull(token);
+
+        #else
+
+        if (token is null)
+            throw new ArgumentNullException(nameof(token));
+
+        #endif
+
+        #if NET8_0_OR_GREATER
+
+        ArgumentException.ThrowIfNullOrWhiteSpace(token);
+
+        #else
+
+        if (string.IsNullOrWhiteSpace(token))
+            throw new ArgumentException("The token cannot be empty or whitespace.", nameof(token));
+
+        #endif
+    }
+}