Separate second-factor verification and delivery from auth (#40)

backend/product/verification/model/verificaton.go

@@ -17,6 +17,9 @@ const (
 	PurposePasswordReset     VerificationPurpose = "password_reset"
 	PurposeMagicLogin        VerificationPurpose = "magic_login"
 	PurposeLogin             VerificationPurpose = "login"
+	PurposeFactorEnrollment  VerificationPurpose = "factor_enrollment"
+	PurposeFactorPreference  VerificationPurpose = "factor_preference"
+	PurposeFactorProof       VerificationPurpose = "factor_proof"
 	PurposePayout            VerificationPurpose = "payout"
 )
 
@@ -36,6 +39,12 @@ func VPFromString(s string) (VerificationPurpose, error) {
 		return PurposeMagicLogin, nil
 	case string(PurposeLogin):
 		return PurposeLogin, nil
+	case string(PurposeFactorEnrollment):
+		return PurposeFactorEnrollment, nil
+	case string(PurposeFactorPreference):
+		return PurposeFactorPreference, nil
+	case string(PurposeFactorProof):
+		return PurposeFactorProof, nil
 	case string(PurposePayout):
 		return PurposePayout, nil
 	default: