Description

Passthrough auth for users in users.toml that don't have a password triggers weird behavior:

1. Connection pool is created and starts sending health checks to database
2. Health checks fail since PgDog can't connect to Postgres without a password

Potential fix

1. Pause pool on creation and resume it when a user connects and provides a password

Potential edge cases

1. When Postgres auth is set to trust, we don't need a password for the user, so it's valid to not provide one and the pool should still be created. Maybe we don't resume it until the user connects anyway?

Reproduce

pgdog.toml

[general]
passthrough_auth = "enabled_plain"

[[databases]]
name = "pgdog"
host = "127.0.0.1"

users.toml

[[users]]
name =  "pgdog"
database = "pgdog"
# Note: no password set.
# It can also be:
# password = "" # Empty string
# We don't differentiate between the two which is bad enough.

Start PgDog and notice the pool being banned on startup.