This paper presents an overview of SBAS L5 message authentication protocols proposed in the last years. We analyze 13 protocols from four sources: Stanford University, the EAST and SPARC projects, and a protocol proposed for the Australian SBAS. The protocols use L5Q, L5I, digital signatures and delayed disclosure based on TESLA. We also analyze figures of merit and weight their importance for the SBAS authentication protocol comparison, including protocol-specific figures AER (Authentication Error Rate), TBA (Time Between Authentications) and latency, and SBAS service figures (accuracy, integrity, continuity, availability). A plan for the definition, assessment and standardization of SBAS message authentication to be carried out by U.S.-EU Working Group C, in cooperation with EUROCAE WG62/RTCA-SC-159, is also outlined, with the goal of a potential addition of SBAS message authentication in the next version of the DFMC standard.