How to Control user registrations directly on sub-sites

Question

Does anybody have Idea to enable a wordpress based multisite user to automatically get access to all sub-sites under same Multi site ?

If I have A Multi-site installation(Also Buddypress enabled) at mysite.com .And the sub-sites created by my friends and their friends are sub1.mysite.com by A, sub2.mysite.com by B ,sub3.mysite.com by C and so on

My friends A and B wants to allow registrations on their websites to run member ship sites like bookmarking sites etc .So every website runs as a separate member ship site.If a User X want to join in sub1.mysite.com .He clicks on 'Register' and will be redirected to the main site and get registered there. He will come back to the sub-site manually entering the URL again.Even if he is an existent user of the Network.The sub-site owner should give him a subscriber or Editor privilege to post or access that sub-site.

I want a functionality that a new person should be able to join directly on any sub-site.If the person is an existent user he should be able to login simply.

The plugin suggested by Andrea is useful but it is only useful to set ' who is eligible to join' .But again the users need to go to main site to registration .Later the sub-site owner should manually set the privileges .Even an existent user doesn't have any privileges to access the sub-site if we use this plugin. Because the sub-site owner should allow the user manually.

My wish is that,the Network owner should have

*An option to control the sub-sites whether or not to allow a specific sub-site to use registrations.

*The sub-site owners also should have option to decide whether to allow a user to register or not.

*This is the basic functionality.A user should able to join if the sub-site owner allow the registration,without out waiting for privilege setup manually.The first two options are available with the plugin. But the third one is not available.

Sorry if the question is too long and wasting your time

Answer 1

Privacy plugin for the one where you want some users to not be able to access certain sites.

http://wordpress.org/extend/plugins/network-privacy/

Answer 2

It seems like you're asking about giving users admin permission for one site but not for all of them?

If you make a new site, you can assign permissions to certain users, and on a different site, that same user can be assigned a different permission, you can even set it so that all other users besides ones you specify are a certain level automatically.

Answer 3

you can make a function that auto logged a certain user with admin capability. you can set them in plugin that work in network mode. (a plugin that initiate as network can not be unplugged by user or other admin who can not access the main blog)