Tencent/WeKnora · error

invalid JWK exponent value

Error message

invalid JWK exponent value

What it means

The decoded JWK exponent does not fit in an int64 (big-endian bytes exceed 8 bytes or overflow), so it cannot become the int exponent of an rsa.PublicKey. RFC 7518 exponents are small (typically 65537 = "AQAB"), so this value is not a usable RSA exponent.

Source

Thrown at internal/application/service/user.go:1861

func (k oidcJWK) rsaPublicKey() (*rsa.PublicKey, error) {
	if !strings.EqualFold(k.Kty, "RSA") {
		return nil, fmt.Errorf("unsupported JWK key type: %s", k.Kty)
	}
	nBytes, err := decodeJWKBase64(k.N)
	if err != nil {
		return nil, fmt.Errorf("invalid JWK modulus: %w", err)
	}
	eBytes, err := decodeJWKBase64(k.E)
	if err != nil {
		return nil, fmt.Errorf("invalid JWK exponent: %w", err)
	}
	if len(nBytes) == 0 || len(eBytes) == 0 {
		return nil, errors.New("empty JWK modulus or exponent")
	}
	eInt := new(big.Int).SetBytes(eBytes)
	if !eInt.IsInt64() {
		return nil, errors.New("invalid JWK exponent value")
	}
	e := int(eInt.Int64())
	if e <= 0 {
		return nil, errors.New("invalid JWK exponent value")
	}
	return &rsa.PublicKey{N: new(big.Int).SetBytes(nBytes), E: e}, nil
}

func (jwks *oidcJWKS) rsaKeyForKid(kid string) (*rsa.PublicKey, error) {
	var usable []oidcJWK
	for _, k := range jwks.Keys {
		if k.Use != "" && !strings.EqualFold(k.Use, "sig") {
			continue
		}
		if k.Kty != "" && !strings.EqualFold(k.Kty, "RSA") {
			continue
		}
		if kid != "" && k.Kid != kid {

View on GitHub (pinned to 988cbb0330)

Solutions

1. Inspect the 'e' field in the JWKS — it should normally be "AQAB" (65537).
2. Re-fetch the JWKS from the provider's canonical jwks_uri.
3. Filter out keys with non-standard exponent encodings before use.
4. If this is a test, fix the fixture so 'e' decodes to a small positive integer.

Example fix

// before
"e": "AAAAAAAAAAAAAAAAAAAAAQAB" // >8 bytes
// after
"e": "AQAB"

eBytes, err := base64.RawURLEncoding.DecodeString(k.E)
if err != nil || len(eBytes) == 0 || len(eBytes) > 8 {
    return fmt.Errorf("JWK %q has invalid exponent", k.Kid)
}

func plausibleExponent(k jwk) bool {
    e, err := base64.RawURLEncoding.DecodeString(k.E)
    return err == nil && len(e) > 0 && len(e) <= 8
}

When it happens

Trigger: decodeJWKBase64(k.E) succeeds but the resulting big.Int does not fit IsInt64() — e.g. 'e' is an absurdly long base64url string in the JWKS entry.

Common situations: Corrupted or maliciously crafted JWKS entries; tests feeding malformed 'e' values; a key with swapped n/e fields.

Related errors

• empty JWK modulus or exponent
• no matching JWKS key for id_token
• JWKS document contains no keys
• OIDC provider returned no user claims
• id_token missing kid and JWKS contains multiple RSA signing

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/7b5ac40d60c4cd2e. Report an issue: GitHub.