A wide-area time authentication algorithm is proposed to compute the Global Positioning System (GPS) timing that is resilient against spoofing attacks. The considered widearea network consists of multiple GPS receiving systems, each comprising of the innovative distributed multiple directional antennas (DMDA) setup triggered via a common clock. Based on the communication infrastructure of the grid, the single-difference pseudorange residuals across the antennas are processed using the wide-area belief propagation-based extended Kalman filter (BP-EKF) algorithm in a distributed manner. To detect spoofing, a KL-divergence-based threshold is used to estimate the dissimilarity in the antenna-specific timing errors. Thereafter, the pseudoranges are corrected using the BP estimates of timing error and processed via adaptive EKF to compute the GPS timing, which is given to the phasor measurement units (PMUs). We have demonstrated the successfully detection and mitigation of the external timing attack, by subjecting one receiving system to a simulated meaconing attack that induces a 60 micro second time delay. Thereafter, by analyzing the voltage stability index of a critical node in the simulated grid, we have also validated the compliance of the proposed wide-area BP-EKF estimated timing with the IEEE-C37.118 standards.