Add GetDocumentOfReceiver endpoint and logging support

Updated DocumentController to include a new GetDocumentOfReceiver
endpoint for retrieving envelope documents. Added authorization
based on the Receiver policy and implemented error handling for
invalid or missing EnvelopeId claims. Integrated ILogger to log
errors and provide detailed diagnostics. Included necessary
namespace imports to support the new functionality.

EnvelopeGenerator.API/Controllers/DocumentController.cs

@@ -1,3 +1,4 @@
+using DigitalData.Auth.Claims;
 using EnvelopeGenerator.API.Controllers.Interfaces;
 using EnvelopeGenerator.API.Extensions;
 using EnvelopeGenerator.Application.Documents.Queries;
@@ -5,6 +6,7 @@ using EnvelopeGenerator.Domain.Constants;
 using MediatR;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using System.Threading.Channels;
 
 namespace EnvelopeGenerator.API.Controllers;
 
@@ -17,7 +19,7 @@ namespace EnvelopeGenerator.API.Controllers;
 [Authorize]
 [ApiController]
 [Route("api/[controller]")]
-public class DocumentController(IMediator mediator, IAuthorizationService authService) : ControllerBase, IAuthController
+public class DocumentController(IMediator mediator, IAuthorizationService authService, ILogger<DocumentController> logger) : ControllerBase, IAuthController
 {
     /// <summary>
     /// 
@@ -60,4 +62,33 @@ public class DocumentController(IMediator mediator, IAuthorizationService authSe
 
         return Unauthorized();
     }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="envelopeKey"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    [HttpGet("{envelopeKey}")]
+    [Authorize(Policy = AuthPolicy.Receiver)]
+    public async Task<IActionResult> GetDocumentOfReceiver(string envelopeKey, CancellationToken cancel)
+    {
+        var envelopeIdStr = User.FindFirst(EnvelopeClaimNames.EnvelopeId)?.Value;
+
+        if (!int.TryParse(envelopeIdStr, out int envelopeId))
+        {
+            logger.LogError(
+                "Inner service error: Failed to parse Envelope ID from claims. Claim '{ClaimName}' had an invalid or missing value: '{ClaimValue}'.",
+                EnvelopeClaimNames.EnvelopeId,
+                envelopeIdStr ?? "null");
+
+            return StatusCode(StatusCodes.Status500InternalServerError, "Inner service error: Invalid envelope claim.");
+        }
+
+        var senderDoc = await mediator.Send(new ReadDocumentQuery() { EnvelopeId = envelopeId }, cancel);
+
+        return senderDoc.ByteData is byte[] senderDocByte
+            ? File(senderDocByte, "application/octet-stream")
+            : NotFound("Document is empty.");
+    }
 }