Define the Advanced Custom Fields Pro license key with a constant

acf-install-license

#!/bin/bash
# Setup ACF Pro to use a license key in wp-config
# 
# 1. Place your license key in a file called .acf-license-key somewhere your ssh user has access to it.
#    Default is in your home directory: ~/.acf-license-key
#    Change the setting below if you need to put it somewhere else
# 2. install this file in /usr/local/bin or someplace in your PATH
# 3. make sure you have WP CLI installed
# 4. run acf-install-license from the root of your wordpress install

# set the license key in wp-config
ACF_LICENSE_KEY=`cat ~/.acf-license-key`
wp config set ACF_PRO_LICENSE $ACF_LICENSE_KEY

# install the mu-plugin
mkdir -p wp-content/mu-plugins
cd wp-content/mu-plugins
wget -O acf_pro_license_constant.php https://gist.githubusercontent.com/petertwise/eeb7dea2531ad204a346e42faba0179a/raw/acf_pro_license_constant.php
cd ../..

wait
echo "✅ License and Plugin Installed
"

acf_pro_license_constant.php

<?php
/*
Plugin Name: ACF Pro License Constant
Plugin URI: https://gist.github.com/petertwise/eeb7dea2531ad204a346e42faba0179a
Description: Enables entering ACF Pro plugin activation codes via wp-config.php
Version: 1.1.2

Allows storing license key info for Advanced Custom Fields Pro in wp-config.php

Especially handy if you're constantly pulling database copies between production/staging/local
and invalidating the license in the process

Usage: Place this in wp-config.php
define('ACF_PRO_LICENSE', 'yourkeyhere' );

*/

/*
ACF Pro License Constant is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 2 of the License, or
any later version.
 
ACF Pro License Constant is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License
along with ACF Pro License Constant. If not, see https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html.
*/

function squarecandy_acf_pro_license_autosave() {
	
	/*
	bail out if: 
		- setting in wp-config doesn't exist
		- setting in wp-config is empty
		- ACF Pro is not installed and activated
		- the existing key matches the setting
	*/
	if ( ! defined( 'ACF_PRO_LICENSE' ) || empty( ACF_PRO_LICENSE ) || ! function_exists( 'acf_pro_get_license_key' ) || acf_pro_get_license_key() === ACF_PRO_LICENSE ) {
		return;
	}
	
	// everything below is modified from advanced-custom-fields-pro/pro/admin/admin-updates.php in the activate_pro_licence function

	// Connect to API.
	$post = array(
		'acf_license'	=> ACF_PRO_LICENSE,
		'acf_version'	=> acf_get_setting('version'),
		'wp_name'		=> get_bloginfo('name'),
		'wp_url'		=> home_url(),
		'wp_version'	=> get_bloginfo('version'),
		'wp_language'	=> get_bloginfo('language'),
		'wp_timezone'	=> get_option('timezone_string'),
	);
	$response = acf_updates()->request('v2/plugins/activate?p=pro', $post);
	
	// Check response is expected JSON array (not string).
	if( is_string($response) ) {
		$response = new WP_Error( 'server_error', esc_html($response) );
	}
	
	// Display error.
	if( is_wp_error($response) ) {
		wp_die( $response->get_error_message() );
	}

	// On success.
	if( $response['status'] == 1 ) {
		
		// Update license.
		acf_pro_update_license( $response['license'] );
		
		// Refresh plugins transient to fetch new update data.
		acf_updates()->refresh_plugins_transient();
		
		// Show notice.
		acf_add_admin_notice( $response['message'], 'success' );
	
	// On failure.	
	} else {
		
		// Show notice.
		acf_add_admin_notice( $response['message'], 'warning' );
	}

}
add_filter( 'admin_init', 'squarecandy_acf_pro_license_autosave' );

Very pleased that this will now be part of ACF PRO as of 5.11:
https://support.advancedcustomfields.com/forums/topic/pro-license-key-in-config/#post-150028

Because they have chosen the exact same constant, you can just remove this drop in plugin and everything should continue to work.

@petertwise this is great news, thanks for the head up 👍🏻