Set the client-side key store. Key store contains client's private keys, and the certificates with their corresponding public keys.
Setting a key store instance resets any {@link #sslContext(javax.net.ssl.SSLContext) SSL context instance}value previously specified.
Note that a custom key store is only required if you want to enable a custom setup of a 2-way SSL connections (client certificate authentication).
@param keyStore client-side key store. Must not be {@code null}.
@param password client key password. Must not be {@code null}.
@return an updated client builder instance.
@throws NullPointerException in case any of the supplied parameters is {@code null}.
@see #sslContext
@see #keyStore(java.security.KeyStore,String)
@see #trustStore