Section 50. From the authorized commencement of an action, counterclaim or other proceeding in any court, or appearance in any proceeding before any state or federal department, board or commission, the attorney who appears for a client in such proceeding shall have a lien for his reasonable fees and expenses upon his client's cause of action, counterclaim or claim, upon the judgment, decree or other order in his client's favor entered or made in such proceeding, and upon the proceeds derived therefrom. Upon request of the client or of the attorney, the court in which the proceeding is pending or, if the proceeding is not pending in a court, the superior court, may determine and enforce the lien; provided, that the provisions of this sentence shall not apply to any case where the method of the determination of attorneys' fees is otherwise expressly provided by statute.