Remove OIDC user regexp check

This commit removes the regular expression check on OIDC usernames.
Although it is not recommended to use any character in a username,
it is possible to create and use them. The tool useradd has the flag
--badname and adduser has --allow-badname and --allow-all-names to
create new users with any character.

Moreover, it is possible to create any username with the rest of
provisioners.

Fixes #1436

authority/provisioner/controller.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"crypto/x509"
 	"net/http"
-	"regexp"
 	"strings"
 	"time"
 
@@ -115,20 +114,18 @@ func DefaultIdentityFunc(_ context.Context, p Interface, email string) (*Identit
 	switch k := p.(type) {
 	case *OIDC:
 		// OIDC principals would be:
-		// ~~1. Preferred usernames.~~ Note: Under discussion, currently disabled
-		// 2. Sanitized local.
-		// 3. Raw local (if different).
-		// 4. Email address.
+		//   ~~1. Preferred usernames.~~ Note: Under discussion, currently disabled
+		//   2. Sanitized local.
+		//   3. Raw local (if different).
+		//   4. Email address.
 		name := SanitizeSSHUserPrincipal(email)
-		if !sshUserRegex.MatchString(name) {
-			return nil, errors.Errorf("invalid principal '%s' from email '%s'", name, email)
-		}
 		usernames := []string{name}
 		if i := strings.LastIndex(email, "@"); i >= 0 {
 			usernames = append(usernames, email[:i])
 		}
 		usernames = append(usernames, email)
 		return &Identity{
+			// Remove duplicated and empty usernames.
 			Usernames: SanitizeStringSlices(usernames),
 		}, nil
 	default:
@@ -178,8 +175,6 @@ func DefaultAuthorizeSSHRenew(_ context.Context, p *Controller, cert *ssh.Certif
 	return nil
 }
 
-var sshUserRegex = regexp.MustCompile("^[a-z][-a-z0-9_]*$")
-
 // SanitizeStringSlices removes duplicated an empty strings.
 func SanitizeStringSlices(original []string) []string {
 	output := []string{}

authority/provisioner/controller_test.go

@@ -167,6 +167,12 @@ func TestController_GetIdentity(t *testing.T) {
 		}}, args{ctx, "jane@doe.org"}, &Identity{
 			Usernames: []string{"jane"},
 		}, false},
+		{"ok badname", fields{&OIDC{}, nil}, args{ctx, "1000@doe.org"}, &Identity{
+			Usernames: []string{"1000", "1000@doe.org"},
+		}, false},
+		{"ok sanitized badname", fields{&OIDC{}, nil}, args{ctx, "1000+10@doe.org"}, &Identity{
+			Usernames: []string{"1000_10", "1000+10", "1000+10@doe.org"},
+		}, false},
 		{"fail provisioner", fields{&JWK{}, nil}, args{ctx, "jane@doe.org"}, nil, true},
 		{"fail custom", fields{&OIDC{}, func(ctx context.Context, p Interface, email string) (*Identity, error) {
 			return nil, fmt.Errorf("an error")

authority/provisioner/provisioner_test.go

@@ -76,13 +76,6 @@ func TestDefaultIdentityFunc(t *testing.T) {
 				err: errors.New("provisioner type '*provisioner.X5C' not supported by identity function"),
 			}
 		},
-		"fail/bad-ssh-regex": func(t *testing.T) test {
-			return test{
-				p:     &OIDC{},
-				email: "$%^#_>@smallstep.com",
-				err:   errors.New("invalid principal '______' from email '$%^#_>@smallstep.com'"),
-			}
-		},
 		"ok": func(t *testing.T) test {
 			return test{
 				p:        &OIDC{},
@@ -142,6 +135,13 @@ func TestDefaultIdentityFunc(t *testing.T) {
 				identity:  &Identity{Usernames: []string{"john", "john@smallstep.com"}},
 			}
 		},
+		"ok/badname": func(t *testing.T) test {
+			return test{
+				p:        &OIDC{},
+				email:    "$%^#_>@smallstep.com",
+				identity: &Identity{Usernames: []string{"______", "$%^#_>", "$%^#_>@smallstep.com"}},
+			}
+		},
 	}
 	for name, get := range tests {
 		t.Run(name, func(t *testing.T) {