GC: User Validation Feature (#1261)

## Description
verifyBackupInputs() is a newly created function that ensures that a selector given to GraphConnector is valid to continue.
Test src file:  `graph_connector_test.go` expanded. 
<!-- Insert PR description-->

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [x] 🐛 Bugfix


## Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
*closes  #1258<issue>

## Test Plan

- [x] ⚡ Unit test

src/internal/connector/graph_connector.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"fmt"
 	"runtime/trace"
+	"strings"
 	"sync"
 
 	"github.com/hashicorp/go-multierror"
@@ -377,9 +378,15 @@ func IsNonRecoverableError(e error) bool {
 	return errors.As(e, &nonRecoverable)
 }
 
+// DataCollections utility function to launch backup operations for exchange and onedrive
 func (gc *GraphConnector) DataCollections(ctx context.Context, sels selectors.Selector) ([]data.Collection, error) {
 	defer trace.StartRegion(ctx, "gc:dataCollections:"+sels.Service.String()).End()
 
+	err := verifyBackupInputs(sels, gc.Users)
+	if err != nil {
+		return nil, err
+	}
+
 	switch sels.Service {
 	case selectors.ServiceExchange:
 		return gc.ExchangeDataCollection(ctx, sels)
@@ -433,3 +440,49 @@ func (gc *GraphConnector) OneDriveDataCollections(
 
 	return collections, errs
 }
+
+func verifyBackupInputs(sel selectors.Selector, mapOfUsers map[string]string) error {
+	var personnel []string
+
+	// retrieve users from selectors
+	switch sel.Service {
+	case selectors.ServiceExchange:
+		backup, err := sel.ToExchangeBackup()
+		if err != nil {
+			return err
+		}
+
+		for _, scope := range backup.Scopes() {
+			temp := scope.Get(selectors.ExchangeUser)
+			personnel = append(personnel, temp...)
+		}
+	case selectors.ServiceOneDrive:
+		backup, err := sel.ToOneDriveBackup()
+		if err != nil {
+			return err
+		}
+
+		for _, user := range backup.Scopes() {
+			temp := user.Get(selectors.OneDriveUser)
+			personnel = append(personnel, temp...)
+		}
+
+	default:
+		return errors.New("service %s not supported")
+	}
+
+	// verify personnel
+	normUsers := map[string]struct{}{}
+
+	for k := range mapOfUsers {
+		normUsers[strings.ToLower(k)] = struct{}{}
+	}
+
+	for _, user := range personnel {
+		if _, ok := normUsers[strings.ToLower(user)]; !ok {
+			return fmt.Errorf("%s user not found within tenant", user)
+		}
+	}
+
+	return nil
+}

src/internal/connector/graph_connector_disconnected_test.go

@@ -204,3 +204,64 @@ func (suite *DisconnectedGraphConnectorSuite) TestRestoreFailsBadService() {
 	assert.Equal(t, 0, status.FolderCount)
 	assert.Equal(t, 0, status.Successful)
 }
+
+func (suite *DisconnectedGraphConnectorSuite) TestVerifyBackupInputs() {
+	users := make(map[string]string)
+	users["elliotReid@someHospital.org"] = ""
+	users["chrisTurk@someHospital.org"] = ""
+	users["carlaEspinosa@someHospital.org"] = ""
+	users["bobKelso@someHospital.org"] = ""
+	users["johnDorian@someHospital.org"] = ""
+
+	tests := []struct {
+		name        string
+		getSelector func(t *testing.T) selectors.Selector
+		checkError  assert.ErrorAssertionFunc
+	}{
+		{
+			name:       "Invalid User",
+			checkError: assert.Error,
+			getSelector: func(t *testing.T) selectors.Selector {
+				sel := selectors.NewOneDriveBackup()
+				sel.Include(sel.Folders([]string{"foo@SomeCompany.org"}, selectors.Any()))
+				return sel.Selector
+			},
+		},
+		{
+			name:       "Valid Single User",
+			checkError: assert.NoError,
+			getSelector: func(t *testing.T) selectors.Selector {
+				sel := selectors.NewExchangeBackup()
+				sel.Include(sel.MailFolders([]string{"bobkelso@someHospital.org"}, selectors.Any()))
+				return sel.Selector
+			},
+		},
+		{
+			name:       "Partial invalid user",
+			checkError: assert.Error,
+			getSelector: func(t *testing.T) selectors.Selector {
+				sel := selectors.NewExchangeBackup()
+				sel.Include(sel.MailFolders([]string{"bobkelso@someHospital.org", "janitor@someHospital.org"}, selectors.Any()))
+				return sel.Selector
+			},
+		},
+		{
+			name:       "Multiple Valid Users",
+			checkError: assert.NoError,
+			getSelector: func(t *testing.T) selectors.Selector {
+				sel := selectors.NewOneDriveBackup()
+				sel.Include(
+					sel.Users([]string{"elliotReid@someHospital.org", "johnDorian@someHospital.org", "christurk@somehospital.org"}))
+
+				return sel.Selector
+			},
+		},
+	}
+
+	for _, test := range tests {
+		suite.T().Run(test.name, func(t *testing.T) {
+			err := verifyBackupInputs(test.getSelector(t), users)
+			test.checkError(t, err)
+		})
+	}
+}

src/internal/connector/graph_connector_test.go

@@ -79,6 +79,44 @@ func (suite *GraphConnectorIntegrationSuite) TestSetTenantUsers() {
 	suite.Greater(len(newConnector.Users), 0)
 }
 
+// TestInvalidUserForDataCollections ensures verification process for users
+func (suite *GraphConnectorIntegrationSuite) TestInvalidUserForDataCollections() {
+	ctx, flush := tester.NewContext()
+	defer flush()
+
+	invalidUser := "foo@example.com"
+	connector := loadConnector(ctx, suite.T())
+	tests := []struct {
+		name        string
+		getSelector func(t *testing.T) selectors.Selector
+	}{
+		{
+			name: "invalid exchange backup user",
+			getSelector: func(t *testing.T) selectors.Selector {
+				sel := selectors.NewExchangeBackup()
+				sel.Include(sel.MailFolders([]string{invalidUser}, selectors.Any()))
+				return sel.Selector
+			},
+		},
+		{
+			name: "Invalid onedrive backup user",
+			getSelector: func(t *testing.T) selectors.Selector {
+				sel := selectors.NewOneDriveBackup()
+				sel.Include(sel.Folders([]string{invalidUser}, selectors.Any()))
+				return sel.Selector
+			},
+		},
+	}
+
+	for _, test := range tests {
+		suite.T().Run(test.name, func(t *testing.T) {
+			collections, err := connector.DataCollections(ctx, test.getSelector(t))
+			assert.Error(t, err)
+			assert.Empty(t, collections)
+		})
+	}
+}
+
 // TestExchangeDataCollection verifies interface between operation and
 // GraphConnector remains stable to receive a non-zero amount of Collections
 // for the Exchange Package. Enabled exchange applications: