users service: add sessions (#17744)

* users: add cache to service

* reflect review comments

app/user_test.go

@@ -27,34 +27,6 @@ import (
 	"github.com/mattermost/mattermost-server/v5/utils/testutils"
 )
 
-func TestCheckUserDomain(t *testing.T) {
-	th := Setup(t).InitBasic()
-	defer th.TearDown()
-
-	user := th.BasicUser
-
-	cases := []struct {
-		domains string
-		matched bool
-	}{
-		{"simulator.amazonses.com", true},
-		{"gmail.com", false},
-		{"", true},
-		{"gmail.com simulator.amazonses.com", true},
-	}
-	for _, c := range cases {
-		matched := CheckUserDomain(user, c.domains)
-		if matched != c.matched {
-			if c.matched {
-				t.Logf("'%v' should have matched '%v'", user.Email, c.domains)
-			} else {
-				t.Logf("'%v' should not have matched '%v'", user.Email, c.domains)
-			}
-			t.FailNow()
-		}
-	}
-}
-
 func TestCreateOAuthUser(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()