  Canonical quantization of the photon -- a free massless vector field -- is
considered in cosmological spacetimes in a two-parameter family of linear
gauges that treat all the vector potential components on equal footing. The
goal is setting up a framework for computing photon two-point functions
appropriate for loop computations in realistic inflationary spacetimes. The
quantization is implemented without relying on spacetime symmetries, but rather
it is based on the classical canonical structure. Special attention is paid to
the quantization of the canonical first-class constraint structure that is
implemented as the condition on the physical states. This condition gives rise
to subsidiary conditions that the photon two-point functions must satisfy. Some
of the de Sitter space photon propagators from the literature are found not to
satisfy these subsidiary conditions, bringing into question their consistency.
