Add claim extension methods for user authentication

Introduce `ReceiverClaimExtensions` and `SenderClaimExtensions` classes in the `EnvelopeGenerator.API.Extensions` namespace. These classes provide methods to extract specific claims from a `ClaimsPrincipal` object, aiding in user authentication.

In `ReceiverClaimExtensions.cs`, add methods to retrieve envelope-specific claims such as `EnvelopeUuid`, `ReceiverSignature`, `ReceiverMail`, `EnvelopeId`, and `ReceiverId`. Implement `GetRequiredClaimValue` to handle missing claims.

In `SenderClaimExtensions.cs`, add methods to extract sender-related claims like `GetId`, `GetUsername`, `GetName`, `GetPrename`, and `GetEmail`. Implement `GetRequiredClaimOfSender` for handling missing claims.

Both classes include XML documentation for clarity on method usage and exceptions.

EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Extensions/ReceiverClaimExtensions.cs

@@ -0,0 +1,96 @@
+using DigitalData.Auth.Claims;
+using Microsoft.IdentityModel.JsonWebTokens;
+using System.Security.Claims;
+
+namespace EnvelopeGenerator.API.Extensions;
+
+/// <summary>
+/// Provides helper methods for working with envelope-specific authentication claims.
+/// </summary>
+public static class ReceiverClaimExtensions
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="user"></param>
+    /// <param name="claimType"></param>
+    /// <returns></returns>
+    /// <exception cref="InvalidOperationException"></exception>
+    private static string GetRequiredClaimValue(this ClaimsPrincipal user, string claimType)
+    {
+        var value = user.FindFirstValue(claimType);
+        if (value is not null)
+        {
+            return value;
+        }
+
+        var identity = user.Identity;
+        var principalName = identity?.Name ?? "(anonymous)";
+        var authType = identity?.AuthenticationType ?? "(none)";
+        var availableClaims = string.Join(", ", user.Claims.Select(c => $"{c.Type}={c.Value}"));
+        var message = $"Required claim '{claimType}' is missing for user '{principalName}' (auth: {authType}). Available claims: [{availableClaims}].";
+        throw new InvalidOperationException(message);
+    }
+
+    private static string GetRequiredClaimValue(this ClaimsPrincipal user, params string[] claimTypes)
+    {
+        foreach (var claimType in claimTypes.Where(t => !string.IsNullOrWhiteSpace(t)).Distinct())
+        {
+            var value = user.FindFirstValue(claimType);
+            if (!string.IsNullOrWhiteSpace(value))
+                return value;
+        }
+
+        var identity = user.Identity;
+        var principalName = identity?.Name ?? "(anonymous)";
+        var authType = identity?.AuthenticationType ?? "(none)";
+        var availableClaims = string.Join(", ", user.Claims.Select(c => $"{c.Type}={c.Value}"));
+        var message = $"Required claim(s) '{string.Join("', '", claimTypes)}' are missing for user '{principalName}' (auth: {authType}). Available claims: [{availableClaims}].";
+        throw new InvalidOperationException(message);
+    }
+
+    /// <summary>
+    /// Gets the authenticated envelope UUID from the claims.
+    /// </summary>
+    public static string EnvelopeUuid(this ClaimsPrincipal user)
+        => user.GetRequiredClaimValue(EnvelopeClaimNames.EnvelopeUuid);
+
+    /// <summary>
+    /// Gets the authenticated receiver signature from the claims.
+    /// </summary>
+    public static string ReceiverSignature(this ClaimsPrincipal user)
+        => user.GetRequiredClaimValue(EnvelopeClaimNames.ReceiverSignature);
+
+    /// <summary>
+    /// Gets the authenticated receiver email address from the claims.
+    /// </summary>
+    public static string ReceiverMail(this ClaimsPrincipal user)
+        => user.GetRequiredClaimValue(JwtRegisteredClaimNames.Email);
+
+    /// <summary>
+    /// Gets the authenticated envelope identifier from the claims.
+    /// </summary>
+    public static int EnvelopeId(this ClaimsPrincipal user)
+    {
+        var envIdStr = user.GetRequiredClaimValue(EnvelopeClaimNames.EnvelopeId);
+        if (int.TryParse(envIdStr, out var envId))
+            return envId;
+        else
+            throw new InvalidOperationException($"Claim '{EnvelopeClaimNames.EnvelopeId}' is not a valid integer.");
+    }
+
+    /// <summary>
+    /// Gets the authenticated receiver identifier from the claims.
+    /// </summary>
+    /// <param name="user"></param>
+    /// <returns></returns>
+    /// <exception cref="InvalidOperationException"></exception>
+    public static int ReceiverId(this ClaimsPrincipal user)
+    {
+        var rcvIdStr = user.GetRequiredClaimValue(EnvelopeClaimNames.ReceiverId);
+        if (int.TryParse(rcvIdStr, out var rcvId))
+            return rcvId;
+        else
+            throw new InvalidOperationException($"Claim '{EnvelopeClaimNames.ReceiverId}' is not a valid integer.");
+    }
+}

EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Extensions/SenderClaimExtensions.cs

@@ -0,0 +1,95 @@
+using System.Security.Claims;
+
+namespace EnvelopeGenerator.API.Extensions
+{
+    /// <summary>
+    /// Provides extension methods for extracting user information from a <see cref="ClaimsPrincipal"/>.
+    /// </summary>
+    public static class SenderClaimExtensions
+    {
+        private static string GetRequiredClaimOfSender(this ClaimsPrincipal user, string claimType)
+        {
+            var value = user.FindFirstValue(claimType);
+            if (value is not null)
+            {
+                return value;
+            }
+
+            var identity = user.Identity;
+            var principalName = identity?.Name ?? "(anonymous)";
+            var authType = identity?.AuthenticationType ?? "(none)";
+            var availableClaims = string.Join(", ", user.Claims.Select(c => $"{c.Type}={c.Value}"));
+            var message = $"Required claim '{claimType}' is missing for user '{principalName}' (auth: {authType}). Available claims: [{availableClaims}].";
+            throw new InvalidOperationException(message);
+        }
+
+        private static string GetRequiredClaimOfSender(this ClaimsPrincipal user, params string[] claimTypes)
+        {
+            string? value = null;
+
+            foreach (var claimType in claimTypes)
+            {
+                value = user.FindFirstValue(claimType);
+                if (value is not null)
+                    return value;
+            }
+
+            var identity = user.Identity;
+            var principalName = identity?.Name ?? "(anonymous)";
+            var authType = identity?.AuthenticationType ?? "(none)";
+            var availableClaims = string.Join(", ", user.Claims.Select(c => $"{c.Type}={c.Value}"));
+            var message = $"Required claim among [{string.Join(", ", claimTypes)}] is missing for user '{principalName}' (auth: {authType}). Available claims: [{availableClaims}].";
+            throw new InvalidOperationException(message);
+        }
+
+        /// <summary>
+        /// Retrieves the user's ID from the claims. Throws an exception if the ID is missing or invalid.
+        /// </summary>
+        /// <param name="user">The <see cref="ClaimsPrincipal"/> representing the user.</param>
+        /// <returns>The user's ID as an integer.</returns>
+        /// <exception cref="InvalidOperationException">Thrown if the user ID claim is missing or invalid.</exception>
+        public static int GetId(this ClaimsPrincipal user)
+        {
+            var idValue = user.GetRequiredClaimOfSender(ClaimTypes.NameIdentifier, "sub");
+
+            if (!int.TryParse(idValue, out var result))
+            {
+                throw new InvalidOperationException("User ID claim is missing or invalid. This may indicate a misconfigured or forged JWT token.");
+            }
+
+            return result;
+        }
+
+        /// <summary>
+        /// Retrieves the username from the claims.
+        /// </summary>
+        /// <param name="user">The <see cref="ClaimsPrincipal"/> representing the user.</param>
+        /// <returns>The username as a string.</returns>
+        public static string GetUsername(this ClaimsPrincipal user)
+            => user.GetRequiredClaimOfSender(ClaimTypes.Name);
+
+        /// <summary>
+        /// Retrieves the user's surname (last name) from the claims.
+        /// </summary>
+        /// <param name="user">The <see cref="ClaimsPrincipal"/> representing the user.</param>
+        /// <returns>The surname as a string.</returns>
+        public static string GetName(this ClaimsPrincipal user)
+            => user.GetRequiredClaimOfSender(ClaimTypes.Surname);
+
+        /// <summary>
+        /// Retrieves the user's given name (first name) from the claims.
+        /// </summary>
+        /// <param name="user">The <see cref="ClaimsPrincipal"/> representing the user.</param>
+        /// <returns>The given name as a string.</returns>
+        public static string GetPrename(this ClaimsPrincipal user)
+            => user.GetRequiredClaimOfSender(ClaimTypes.GivenName);
+
+        /// <summary>
+        /// Retrieves the user's email address from the claims.
+        /// </summary>
+        /// <param name="user">The <see cref="ClaimsPrincipal"/> representing the user.</param>
+        /// <returns>The email address as a string.</returns>
+        public static string GetEmail(this ClaimsPrincipal user)
+            => user.GetRequiredClaimOfSender(ClaimTypes.Email);
+    }
+}