Configuration is handled by Viper, which supports many ways of setting config values.
As a general rule, Prebid Server will log its resolved config values on startup and exit immediately if they're not valid.
For development, it's easiest to define your config inside a pbs.yaml file in the project root.
For now, see the contract classes in the code.
Also note that Viper will also read environment variables for config values. Prebid Server will look for the prefix PBS_ on the environment variables, and map underscores (_)
to periods. For example, to set host_cookie.ttl_days via an environment variable, set PBS_HOST_COOKIE_TTL_DAYS to the desired value.