Eaglecraft allows players to upload custom skin files manually or fetch them via Mojang usernames.
Because EagleCraft is popular, many fake websites exist that bundle malware, adware, or actual cheat clients (which will get you banned). You must know the official source. eaglecraft 1.12.2 download
Look for the index.html or a "Standalone" version of the 1.12.2 build. Eaglecraft allows players to upload custom skin files