Sets an external command to be invoked when a passphrase for decrypting an SSL file such as a private key needs to be obtained. By default, this parameter is empty, which means the built-in prompting mechanism is used.
The command must print the passphrase to the standard output and exit with code 0. In the parameter value,
%p is replaced by a prompt string. (Write
%% for a literal
%.) Note that the prompt string will probably contain whitespace, so be sure to quote adequately. A single newline is stripped from the end of the output if present.
The command does not actually have to prompt the user for a passphrase. It can read it from a file, obtain it from a keychain facility, or similar. It is up to the user to make sure the chosen mechanism is adequately secure.
This parameter can only be set in the postgresql.conf file or on the server command line.