Another free community add-on - wonderful! - with suggestion that might solve some potential issues
May I suggest you change the name of
class.googlesignin.plugin.php to either default.php or class.steamsignin.plugin.php
in the steamsignin plugin (unless for some reason
the name class.googlesignin.plugin.php) is required.
Seems like a good idea to me to have distinct names for class.xxxx.plugin.php files if for no other reason than to prevent future potential clashes.
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.