Allow Host request header to override the http request host (#440)

* Add `allow_host_override` attribute that allows the `Host` request header to override the request host.

* Remove duplicate host override

* Add changelog entry

* Update provider documentation

* Remove feature flag for host overrides

* Update documentation

* Apply suggestions from code review

Co-authored-by: Austin Valle <austinvalle@gmail.com>

* Set `request.Host` in the same loop setting the request headers.

* Add note changelog describing functionality change.

---------

Co-authored-by: Austin Valle <austinvalle@gmail.com>

.changes/unreleased/BUG FIXES-20240719-143606.yaml

@@ -0,0 +1,5 @@
+kind: BUG FIXES
+body: 'data-source/http: Allow `Host` header in `request_headers` to be set on HTTP request'
+time: 2024-07-19T14:36:06.795798-04:00
+custom:
+  Issue: "440"

.changes/unreleased/NOTES-20240723-162543.yaml

@@ -0,0 +1,17 @@
+kind: NOTES
+body: |+
+  data-source/http: Previous versions of this provider ignored any `Host` headers specified in the `request_headers` attribute when setting the HTTP request. Any specified `Host` request headers will now override the `url` attribute host.
+  
+  For example, in the following configuration:
+  ```hcl
+  data "http" "example" {
+    url      = "https://www.example.com"
+    request_headers = {
+      Host = "www.differentexample.com"
+    }
+  }
+  ```
+  The HTTP request host will now be `www.differentexample.com` instead of `www.example.com`.
+time: 2024-07-23T16:25:43.160519-04:00
+custom:
+  Issue: "440"

internal/provider/data_source_http.go

@@ -315,6 +315,9 @@ func (d *httpDataSource) Read(ctx context.Context, req datasource.ReadRequest, r
 		}
 
 		request.Header.Set(name, header)
+		if name == "Host" {
+			request.Host = header
+		}
 	}
 
 	response, err := retryClient.Do(request)

internal/provider/data_source_http_test.go

@@ -602,6 +602,49 @@ func TestDataSource_UnsupportedInsecureCaCert(t *testing.T) {
 	})
 }
 
+func TestDataSource_HostRequestHeaderOverride_200(t *testing.T) {
+	altHost := "alt-test-host"
+
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Host != altHost {
+			w.WriteHeader(400)
+			return
+		}
+
+		w.Header().Set("Content-Type", "text/plain")
+		w.Header().Set("X-Single", "foobar")
+		w.Header().Add("X-Double", "1")
+		w.Header().Add("X-Double", "2")
+		_, err := w.Write([]byte("1.0.0"))
+		if err != nil {
+			t.Errorf("error writing body: %s", err)
+		}
+	}))
+	defer testServer.Close()
+
+	resource.ParallelTest(t, resource.TestCase{
+		ProtoV5ProviderFactories: protoV5ProviderFactories(),
+		Steps: []resource.TestStep{
+			{
+				Config: fmt.Sprintf(`
+							data "http" "http_test" {
+								url = "%s"
+								request_headers = {
+									"Host" = "%s"
+								}
+							}`, testServer.URL, altHost),
+				Check: resource.ComposeTestCheckFunc(
+					resource.TestCheckResourceAttr("data.http.http_test", "status_code", "200"),
+					resource.TestCheckResourceAttr("data.http.http_test", "response_body", "1.0.0"),
+					resource.TestCheckResourceAttr("data.http.http_test", "response_headers.Content-Type", "text/plain"),
+					resource.TestCheckResourceAttr("data.http.http_test", "response_headers.X-Single", "foobar"),
+					resource.TestCheckResourceAttr("data.http.http_test", "response_headers.X-Double", "1, 2"),
+				),
+			},
+		},
+	})
+}
+
 // testProxiedURL is a hardcoded URL used in acceptance testing where it is
 // expected that a locally started HTTP proxy will handle the request.
 //