When you write script that need to perform remote authentication you don't want to include passwords plain text in the script itself. And if the credentials are personal credentials you cannot deliver them with the script anyway.

libsecret

Since 2008 the Secret Service API is standardized via freedesktop.org and is implemented by GnomeKeyring and ksecretservice. Effectivly there is standard interface to access secrets on Linux desktops. Sadly the CLI tools are rarely installed by default so you have to add them manually. On Debian 
apt install libsecret-tools

Using secret-tool

There are two important modes:

Fetching passwords

The "lookup" command prints the password to STDOUT 
/usr/bin/secret-tool lookup <key> <name>

Storing passwords

Note that with "store" you do not pass the password, as a dialog is raised to add it. 
/usr/bin/secret-tool store <key> <name>

Scripting with secret-tool

Here is a simple example Bash script to automatically ask, store and use a secret: 
#!/bin/bash


ST=/usr/bin/secret-tool
LOGIN="my-login"		# Unique id for your login
LABEL="My special login"	# Human readable label

get_password() {
   $ST lookup "$LOGIN" "$USER"
}

password=$( get_password )
if [ "$password" = "" ]; then
    $ST store --label "$LABEL" "$LOGIN" "$USER"
    password=$( get_password )
fi

if [ "$password" = "" ]; then
    echo "ERROR: Failed to fetch password!"
else
    echo "Credentials: user=$USER password=$password"
fi
Note that the secret will appear in the "Login" keyring. On GNOME you can check the secret with "seahorse".