diff --git a/oauthproxy.go b/oauthproxy.go
index 653701d9..9f80f643 100644
--- a/oauthproxy.go
+++ b/oauthproxy.go
@@ -364,13 +364,13 @@ func (p *OAuthProxy) enrichSession(ctx context.Context, s *sessionsapi.SessionSt
 	var err error
 	if s.Email == "" {
 		s.Email, err = p.provider.GetEmailAddress(ctx, s)
-		if err != nil && err.Error() != "not implemented" {
+		if err != nil && !errors.Is(err, providers.ErrNotImplemented) {
 			return err
 		}
 	}
 	if s.User == "" {
 		s.User, err = p.provider.GetUserName(ctx, s)
-		if err != nil && err.Error() != "not implemented" {
+		if err != nil && !errors.Is(err, providers.ErrNotImplemented) {
 			return err
 		}
 	}
diff --git a/providers/provider_default.go b/providers/provider_default.go
index 8a5a98ac..4e96f0e0 100644
--- a/providers/provider_default.go
+++ b/providers/provider_default.go
@@ -14,7 +14,13 @@ import (
 	"github.com/oauth2-proxy/oauth2-proxy/v7/pkg/requests"
 )
 
-var _ Provider = (*ProviderData)(nil)
+var (
+	// ErrNotImplemented is returned when a provider did not override a default
+	// implementation method that doesn't have sensible defaults
+	ErrNotImplemented = errors.New("not implemented")
+
+	_ Provider = (*ProviderData)(nil)
+)
 
 // Redeem provides a default implementation of the OAuth2 token redemption process
 func (p *ProviderData) Redeem(ctx context.Context, redirectURL, code string) (s *sessions.SessionState, err error) {
@@ -82,12 +88,12 @@ func (p *ProviderData) GetLoginURL(redirectURI, state string) string {
 
 // GetEmailAddress returns the Account email address
 func (p *ProviderData) GetEmailAddress(ctx context.Context, s *sessions.SessionState) (string, error) {
-	return "", errors.New("not implemented")
+	return "", ErrNotImplemented
 }
 
 // GetUserName returns the Account username
 func (p *ProviderData) GetUserName(ctx context.Context, s *sessions.SessionState) (string, error) {
-	return "", errors.New("not implemented")
+	return "", ErrNotImplemented
 }
 
 // ValidateGroup validates that the provided email exists in the configured provider
@@ -110,5 +116,5 @@ func (p *ProviderData) RefreshSessionIfNeeded(ctx context.Context, s *sessions.S
 // CreateSessionStateFromBearerToken should be implemented to allow providers
 // to convert ID tokens into sessions
 func (p *ProviderData) CreateSessionStateFromBearerToken(ctx context.Context, rawIDToken string, idToken *oidc.IDToken) (*sessions.SessionState, error) {
-	return nil, errors.New("not implemented")
+	return nil, ErrNotImplemented
 }