A common parameterization is to assume the equation of state parameter w = p/rho = constant. As of April 2003 CAMB includes this parameterization by default. It assumes that Omega_Lambda is Omega_Quintessence, with constant equation of state w (i.e. you can't have Lambda and quintessence).
There is also a more general quintessence class that lets you specific a single scalar field potential. As of Camb 1.2 (2020) this is part of the main CAMB code.