static AccessTokenRequest ofResourceOwnerPassword(String username, String password,
                                                      ClientAuthentication clientAuthentication) {
        requireNonNull(clientAuthentication, "clientAuthentication");
        return ofResourceOwnerPassword(username, password, clientAuthentication, null);
    }
Creates a new {@link AccessTokenRequest} that is used to request an access token using the resource owner
password credentials with the {@link ClientAuthentication}, as per
<a href="https://datatracker.ietf.org/doc/html/rfc6749#section-4.3">RFC 6749, Section 4.3</a>.
oauth2/src/main/java/com/linecorp/armeria/client/auth/oauth2/AccessTokenRequest.java