grafana/k6 · error

failed to parse input as EC JWK key: %w

Error message

failed to parse input as EC JWK key: %w

What it means

importECDSAJWK first unmarshals the JWK bytes into the internal ecJWK struct; this error means that JSON unmarshaling failed. In k6 the JWK is passed as a JavaScript object which is re-serialized with json.Marshal, so a valid object almost never fails here — the failure comes from fields having the wrong JSON type (ecJWK expects kty/crv/x/y/d to be strings). The wrapped %w carries Go's precise 'json: cannot unmarshal ...' message.

Source

Thrown at internal/js/modules/k6/webcrypto/jwk.go:224

	}

	exported.Set("crv", curveParams.Name)
	curveBits := curveParams.BitSize

	exported.Set("x", base64URLEncode(x.Bytes()))
	exported.Set("y", base64URLEncode(y.Bytes()))

	if d != nil {
		exported.Set("d", encodeCurveBigInt(d, curveBits))
	}

	return exported, nil
}

func importECDSAJWK(_ EllipticCurveKind, jsonKeyData []byte) (any, CryptoKeyType, error) {
	var jwkKey ecJWK
	if err := json.Unmarshal(jsonKeyData, &jwkKey); err != nil {
		return nil, UnknownCryptoKeyType, fmt.Errorf("failed to parse input as EC JWK key: %w", err)
	}

	if err := jwkKey.validate(); err != nil {
		return nil, UnknownCryptoKeyType, fmt.Errorf("invalid EC JWK key: %w", err)
	}

	crv, err := pickEllipticCurve(jwkKey.Crv)
	if err != nil {
		return nil, UnknownCryptoKeyType, fmt.Errorf("failed to parse elliptic curve: %w", err)
	}

	x, err := base64URLDecode(jwkKey.X)
	if err != nil {
		return nil, UnknownCryptoKeyType, fmt.Errorf("failed to decode X coordinate: %w", err)
	}

	y, err := base64URLDecode(jwkKey.Y)
	if err != nil {

View on GitHub (pinned to 93accf6570)

Solutions

1. Pass a plain JavaScript object as keyData, not a JSON string
2. Ensure kty, crv, x, y and d are all strings
3. If the JWK arrives as text, JSON.parse it before calling importKey
4. Log the wrapped cause after 'failed to parse input as EC JWK key:' to identify the offending field

Example fix

// before
const key = await crypto.subtle.importKey('jwk', JSON.stringify(jwk), alg, true, ['verify']);
// after
const key = await crypto.subtle.importKey('jwk', jwk, alg, true, ['verify']);

function isPlainObject(v) { return v !== null && typeof v === 'object' && !Array.isArray(v); }
function looksLikeEcJwk(v) {
  return isPlainObject(v) && ['kty','crv','x','y'].every(f => v[f] === undefined || typeof v[f] === 'string');
}
// before import:
if (!looksLikeEcJwk(jwk)) throw new Error('pass a JWK object with string fields, not JSON text');

function isEcJwkShape(v) {
  return v !== null && typeof v === 'object' && !Array.isArray(v) &&
    Object.entries(v).every(([k, val]) =>
      ['kty','crv','x','y','d'].includes(k) ? typeof val === 'string' : true);
}

try {
  key = await crypto.subtle.importKey('jwk', jwk, alg, true, usages);
} catch (e) {
  if (e.message.includes('failed to parse input as EC JWK key')) {
    throw new Error('JWK must be a plain object with string fields (got: ' + e.message + ')');
  }
  throw e;
}

When it happens

Trigger: crypto.subtle.importKey('jwk', keyData, {name:'ECDSA', namedCurve:...}, ...) where keyData is a JSON string instead of an object (double encoding makes the top level a string), or where x/y/crv/d are numbers/arrays/objects instead of strings, or where keyData is an array.

Common situations: Passing JSON.stringify-ed JWKs into importKey (habit from Node's crypto where raw strings are used); JWKs from external services that emit coordinates as byte arrays; script authors building JWKs programmatically with numeric fields.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• invalid EC JWK key: %w
• failed to parse elliptic curve: %w
• failed to decode X coordinate: %w
• failed to decode Y coordinate: %w
• failed to decode D: %w

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/8839862c397f31e1. Report an issue: GitHub.