verify: add context to algorithm mismatch error

Author: gbrlsnchs

verify.go

@@ -2,11 +2,12 @@ package jwt
 
 import (
 	"bytes"
-	"errors"
+
+	"github.com/gbrlsnchs/jwt/v3/internal"
 )
 
 // ErrAlgValidation indicates an incoming JWT's "alg" field mismatches the Validator's.
-var ErrAlgValidation = errors.New(`"alg" field mismatch`)
+var ErrAlgValidation = internal.NewError(`invalid "alg" field`)
 
 // VerifyOption is a functional option for verifying.
 type VerifyOption func(*RawToken) error
@@ -54,7 +55,7 @@ func Verify(token []byte, alg Algorithm, payload interface{}, opts ...VerifyOpti
 // in the JOSE header is the same used by the algorithm.
 func ValidateHeader(rt *RawToken) error {
 	if rt.alg.Name() != rt.hd.Algorithm {
-		return ErrAlgValidation
+		return internal.Errorf("jwt: %q: %w", rt.hd.Algorithm, ErrAlgValidation)
 	}
 	return nil
 }