Support parsing `use_sidechannel` API response field

This field will act as a feature flag that controls whether
gitlab-shell uses the old SSHUploadPack RPC or the new
SSHUploadPackWithSidechannel.

internal/gitlabnet/accessverifier/client.go

@@ -32,10 +32,11 @@ type Request struct {
 }
 
 type Gitaly struct {
-	Repo     pb.Repository     `json:"repository"`
-	Address  string            `json:"address"`
-	Token    string            `json:"token"`
-	Features map[string]string `json:"features"`
+	Repo           pb.Repository     `json:"repository"`
+	Address        string            `json:"address"`
+	Token          string            `json:"token"`
+	Features       map[string]string `json:"features"`
+	UseSidechannel bool              `json:"use_sidechannel"`
 }
 
 type CustomPayloadData struct {

internal/gitlabnet/accessverifier/client_test.go

@@ -86,6 +86,41 @@ func TestSuccessfulResponses(t *testing.T) {
 	}
 }
 
+func TestSidechannelFlag(t *testing.T) {
+	okResponse := testResponse{body: responseBody(t, "allowed_sidechannel.json"), status: http.StatusOK}
+	client := setup(t,
+		map[string]testResponse{"first": okResponse},
+		map[string]testResponse{"1": okResponse},
+	)
+
+	testCases := []struct {
+		desc string
+		args *commandargs.Shell
+		who  string
+	}{
+		{
+			desc: "Provide key id within the request",
+			args: &commandargs.Shell{GitlabKeyId: "1"},
+			who:  "key-1",
+		}, {
+			desc: "Provide username within the request",
+			args: &commandargs.Shell{GitlabUsername: "first"},
+			who:  "user-1",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			result, err := client.Verify(context.Background(), tc.args, uploadPackAction, repo)
+			require.NoError(t, err)
+
+			response := buildExpectedResponse(tc.who)
+			response.Gitaly.UseSidechannel = true
+			require.Equal(t, response, result)
+		})
+	}
+}
+
 func TestGeoPushGetCustomAction(t *testing.T) {
 	client := setup(t, map[string]testResponse{
 		"custom": {

internal/testhelper/testdata/testroot/responses/allowed_sidechannel.json

+{
+	"status": true,
+	"gl_repository": "project-26",
+	"gl_project_path": "group/private",
+	"gl_id": "user-1",
+	"gl_username": "root",
+	"git_config_options": ["option"],
+	"gitaly": {
+		"repository": {
+			"storage_name": "default",
+			"relative_path": "@hashed/5f/9c/5f9c4ab08cac7457e9111a30e4664920607ea2c115a1433d7be98e97e64244ca.git",
+			"git_object_directory": "path/to/git_object_directory",
+			"git_alternate_object_directories": ["path/to/git_alternate_object_directory"],
+			"gl_repository": "project-26",
+			"gl_project_path": "group/private"
+		},
+		"address": "unix:gitaly.socket",
+		"token": "token",
+               "use_sidechannel": true
+	},
+	"git_protocol": "protocol",
+	"gl_console_messages": ["console", "message"]
+}