This is extremely common practice already, think database connections on servers with most keys stored in plain text on the server, there is little way around it.
You just have to prepare your self for automation:
- Ensure the connection is only 443 (SSL or what ever port the SSL is on for this service)
- if you access the server physically ensure you only have the required ports open to complete the tasks the server requires.
- if you have to SSH to the server ensure you use a password and a cert for the connection
it is as the comments say, secure the server and its activities, do not focus on the password, just ensure its not in a publicly touchable file (away from any web servers) and read only for the user who needs to read it with no permissions to anyone else.
The only list of concerns would be this:
- automated logins mean automated connections, you need to ensure you are not getting MitM attacked by putting extra security in, its easier to attack an automated connection (no one there to read the warnings!!)
- Where, when and who can read that password file.
- security of the server and who can access it
dont forget to ensure that all your passwords are randomly generated and stored in an encrypted keychain if you have a cert then 8 random characters will be enough :)