This field is used to store values that don't fit in with any particular set of credentials, but are still unique to a user. Any string based key/value pair can be added to the secrets section of the user config and accessed in the deployment configuration via merge fields. Ex: [credential:secrets:database_password] using the configuration below, would become supersecurepassword.
{
"secrets": {
"database_password": "supersecurepassword"
}
}