I can cover some of thse:
*phpMyAdmin
This is an open source database manager for MySQL databases - it won't work for what you want.
*SAML *OpenID
From the page you link it looks like you know about these two; i.e. they
act as sign in gateways.
OpenID is more "indie", SAML is more "enterprise" - otherwise there are not major differences in what they can achieve.
The major bar to entry is getting the providers to add the ability to sign in using one of these methods.
I'd personally recommend selecting OpenID as it could then be used for a wider variety of logins around the web.
AFAIK resources like Athens (i.e. similar to what you appear to want) tend to use SAML.
*OpenVPN
VPN means setting up access to a pre-authorised network - which then means you can access the restricted resource. I don't think it fits your use case.
Tom