public OAuth2ClientCredentialsGrant build() {
        final ClientAuthentication clientAuthentication = buildClientAuthentication();
        // clientAuthentication is required for this Grant flow
        requireNonNull(clientAuthentication, "clientAuthentication");
        final AccessTokenRequest accessTokenRequest =
                AccessTokenRequest.ofClientCredentials(clientAuthentication);
        delegate().accessTokenRequest(accessTokenRequest);
        final OAuth2AuthorizationGrant delegate = delegate().build();
        return new OAuth2ClientCredentialsGrant(delegate);
    }
Builds a new instance of {@link OAuth2ClientCredentialsGrant} using configured parameters.
oauth2/src/main/java/com/linecorp/armeria/client/auth/oauth2/OAuth2ClientCredentialsGrantBuilder.java