Add a third principal on OIDC tokens with the raw local part of the email.

For the email first.last@example.com it will create the principals
  ["firstlast", "first.last", "first.last@example.com"]

Fixes #253, #254

authority/provisioner/provisioner.go

@@ -336,11 +336,24 @@ type GetIdentityFunc func(ctx context.Context, p Interface, email string) (*Iden
 func DefaultIdentityFunc(ctx context.Context, p Interface, email string) (*Identity, error) {
 	switch k := p.(type) {
 	case *OIDC:
+		// OIDC principals would be:
+		// 1. Sanitized local.
+		// 2. Raw local (if different).
+		// 3. Email address.
 		name := SanitizeSSHUserPrincipal(email)
 		if !sshUserRegex.MatchString(name) {
 			return nil, errors.Errorf("invalid principal '%s' from email '%s'", name, email)
 		}
-		return &Identity{Usernames: []string{name, email}}, nil
+		usernames := []string{name}
+		if i := strings.LastIndex(email, "@"); i >= 0 {
+			if local := email[:i]; !strings.EqualFold(local, name) {
+				usernames = append(usernames, local)
+			}
+		}
+		usernames = append(usernames, email)
+		return &Identity{
+			Usernames: usernames,
+		}, nil
 	default:
 		return nil, errors.Errorf("provisioner type '%T' not supported by identity function", k)
 	}

authority/provisioner/provisioner_test.go

@@ -85,7 +85,28 @@ func TestDefaultIdentityFunc(t *testing.T) {
 			return test{
 				p:        &OIDC{},
 				email:    "max.furman@smallstep.com",
-				identity: &Identity{Usernames: []string{"maxfurman", "max.furman@smallstep.com"}},
+				identity: &Identity{Usernames: []string{"maxfurman", "max.furman", "max.furman@smallstep.com"}},
+			}
+		},
+		"ok letter case": func(t *testing.T) test {
+			return test{
+				p:        &OIDC{},
+				email:    "Max.Furman@smallstep.com",
+				identity: &Identity{Usernames: []string{"maxfurman", "Max.Furman", "Max.Furman@smallstep.com"}},
+			}
+		},
+		"ok simple": func(t *testing.T) test {
+			return test{
+				p:        &OIDC{},
+				email:    "john@smallstep.com",
+				identity: &Identity{Usernames: []string{"john", "john@smallstep.com"}},
+			}
+		},
+		"ok simple letter case": func(t *testing.T) test {
+			return test{
+				p:        &OIDC{},
+				email:    "John@smallstep.com",
+				identity: &Identity{Usernames: []string{"john", "John@smallstep.com"}},
 			}
 		},
 	}