Implement wrapper around M365 helper methods (#825)

## Description

Exports functionality useful for external services/validators

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🐹 Trivial/Minor

## Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/pkg/services/m365/m365.go

@@ -0,0 +1,19 @@
+package m365
+
+import (
+	"github.com/pkg/errors"
+
+	"github.com/alcionai/corso/src/internal/connector"
+	"github.com/alcionai/corso/src/pkg/account"
+)
+
+// Users returns a list of users in the specified M365 tenant
+// TODO: Implement paging support
+func Users(m365Account account.Account) ([]string, error) {
+	gc, err := connector.NewGraphConnector(m365Account)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not initialize M365 graph connection")
+	}
+
+	return gc.GetUsers(), nil
+}

src/pkg/services/m365/m365_test.go

@@ -0,0 +1,40 @@
+package m365
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/stretchr/testify/suite"
+
+	"github.com/alcionai/corso/src/internal/tester"
+)
+
+type M365IntegrationSuite struct {
+	suite.Suite
+}
+
+func TestM365IntegrationSuite(t *testing.T) {
+	if err := tester.RunOnAny(
+		tester.CorsoCITests,
+	); err != nil {
+		t.Skip(err)
+	}
+
+	suite.Run(t, new(M365IntegrationSuite))
+}
+
+func (suite *M365IntegrationSuite) SetupSuite() {
+	_, err := tester.GetRequiredEnvSls(
+		tester.M365AcctCredEnvs)
+	require.NoError(suite.T(), err)
+}
+
+func (suite *M365IntegrationSuite) TestUsers() {
+	acct := tester.NewM365Account(suite.T())
+
+	users, err := Users(acct)
+	require.NoError(suite.T(), err)
+
+	require.NotNil(suite.T(), users)
+	require.Greater(suite.T(), len(users), 0)
+}