Ability to access certificate extensions through `Crypto` API `X509Certificate` class

What is the problem this feature will solve?

Key usages (not extend) are completely different and can only be accessed through certificate extension under OID 2.5.29.15 which contains value in a bit array format.

Key usage can have for definition: Digital signature, Non-repudiation, Key encipherment, Data encipherment, Key agreement, Certificate signing, CRL signing, Encipher only, Decipher only.

As of now Crypto API only provides access to Extended Key usage under the x509.keyUsage but does not provide access to the Key Usage through the certificate Extensions part.

What is the feature you are proposing to solve the problem?

Having a method the class x509 that can allow to have access to the Extension part of a certificate through a safe structure.

What alternatives have you considered?

Using 3rd party libraries like PKIjs or Forge, but I would like a native feature instead.

Node.js Crypto API の X509Certificate 実装と、既存の x509.keyUsage の動作から始めます。証明書拡張と OID 2.5.29.15 がどのように表現されているかを確認し、そのうえで key usage を公開するための安全な構造を定義し、新しい API が key usage と extended key usage を区別していることを検証します。