The board of directors, except as otherwise provided by the bylaws, may authorize any officer or officers, agent or agents, to enter into any contract or execute any instrument in the name and on behalf of the corporation. Such authority may be general or confined to specific instances. Unless so authorized by the board of directors, no officer, agent or employee shall have any power or authority to bind the corporation by any contract, or to pledge its credit, or to render it liable for any purpose or to any amount.