  Context: Accurate distance measurements are fundamental to the study of
Planetary Nebulae (PNe) but have long been elusive. The most accurate and
model-independent distance measurements for galactic PNe come from the
trigonometric parallaxes of their central stars, which were only available for
a few tens of objects prior to the Gaia mission.
  Aims: Accurate identification of PN central stars in the Gaia source
catalogues is a critical prerequisite for leveraging the unprecedented scope
and precision of the trigonometric parallaxes measured by Gaia. Our aim is to
build a complete sample of PN central star detections with minimal
contamination.
  Methods: We develop and apply an automated technique based on the likelihood
ratio method to match candidate central stars in Gaia Data Release 2 (DR2) to
known PNe in the Hong Kong/AAO/Strasbourg H$\alpha$ (HASH) PN catalogue, taking
into account the BP--RP colours of the \emph{Gaia} sources as well as their
positional offsets from the nebula centres. These parameter distributions for
both true central stars and background sources are inferred directly from the
data.
  Results: We present a catalogue of over 1000 Gaia sources that our method has
automatically identified as likely PN central stars. We demonstrate how the
best matches enable us to trace nebula and central star evolution and to
validate existing statistical distance scales, and discuss the prospects for
further refinement of the matching based on additional data. We also compare
the accuracy of our catalogue to that of previous works.
