Add ResponseHeadersVariable Parameter to Invoke-RestMethod (PowerShell#4888)

* Add ResponseHeadersVariable to Invoke-RestMethod

* Add Tests for -ResponseHeadersVariable

* [Feature] Run Feature Tests

* Remove test to address PR feedback

* Alais HV -> RHV per request

* [Feature] Rerun CI

* [Feature] Remove Superfluous Assertion

Author: markekraus

src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/Common/InvokeRestMethodCommand.Common.cs

@@ -60,6 +60,13 @@ public int MaximumFollowRelLink
             set { base._maximumFollowRelLink = value; }
         }
 
+        /// <summary>
+        /// Gets or sets the ResponseHeadersVariable property.
+        /// </summary>
+        [Parameter]
+        [Alias("RHV")]
+        public string ResponseHeadersVariable { get; set; }
+
         #endregion Parameters
 
         #region Helper Methods

src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/CoreCLR/InvokeRestMethodCommand.CoreClr.cs

@@ -95,6 +95,12 @@ internal override void ProcessResponse(HttpResponseMessage response)
                 {
                     StreamHelper.SaveStreamToFile(responseStream, QualifiedOutFile, this);
                 }
+
+                if (!String.IsNullOrEmpty(ResponseHeadersVariable))
+                {
+                    PSVariableIntrinsics vi = SessionState.PSVariable;
+                    vi.Set(ResponseHeadersVariable, WebResponseHelper.GetHeadersDictionary(response));
+                }
             }
         }
 

test/powershell/Modules/Microsoft.PowerShell.Utility/WebCmdlets.Tests.ps1

@@ -2055,6 +2055,26 @@ Describe "Invoke-RestMethod tests" -Tags "Feature" {
 
     #endregion charset encoding tests
 
+    Context 'Invoke-RestMethod ResponseHeadersVariable Tests' {
+        It "Verifies Invoke-RestMethod supports -ResponseHeadersVariable" {
+            $uri = Get-WebListenerUrl -Test '/'
+            $response = Invoke-RestMethod -Uri $uri -ResponseHeadersVariable 'headers'
+
+            $headers.'Content-Type' | Should Be 'text/html; charset=utf-8'
+            $headers.Server | Should Be 'Kestrel'
+        }
+        
+        It "Verifies Invoke-RestMethod supports -ResponseHeadersVariable overwriting existing variable" {
+            $uri = Get-WebListenerUrl -Test '/'
+            $headers = 'prexisting'
+            $response = Invoke-RestMethod -Uri $uri -ResponseHeadersVariable 'headers'
+
+            $headers | Should Not Be 'prexisting'
+            $headers.'Content-Type' | Should Be 'text/html; charset=utf-8'
+            $headers.Server | Should Be 'Kestrel'
+        }
+    }
+
     BeforeEach {
         if ($env:http_proxy) {
             $savedHttpProxy = $env:http_proxy