Purpose

In case you want to grant access to one space only to a specific Confluence user (member of the confluence-users group) but don't want to edit permissions for each space manually. Especially useful when you have a lot of space in your Confluence instance.

Steps for Confluence Cloud

1. Go to User Management.
2. Click on the Users tab, and click on the user's Full Name.
3. Once you're on the user's page, remove the user from the confluence-users group.
4. Now click on the Groups tab in the left menu.
5. Create a group that will only contain this particular user, you can name it however you like.
6. Add the user to this group by clicking on the Add button on the right.
7. From the User management go to Product access > Product access.
8. In the Confluence section, add your group and make sure it has the Can sign-in checkbox checked.
9. Go back to Confluence administration and in the Space Permissions, make sure that the group you created is not listed in the Default Space Permissions.
10. On the same page, locate the space you wish to grant this user access to and click on Manage Permissions. This will lead you to the space permissions page.
11. Click on the Edit Permissions button below the list of groups.
12. In the text box, enter the name of the group you created and click Add.
13. Set the correct permissions you wish this group to have then click on Save All at the bottom of the page.

Steps for Confluence Server and Data Center

1. Go to  > User Management.
2. Search for the user and click on the user's Full Name.
3. Once you're on the user's page, click on Edit Groups, remove the user from the confluence-users group, and Save.
   Please note that this step refers to confluence-users group membership that belongs to the Confluence Internal Directory. 
4. Now click on the Groups tab in the left menu.
5. Create a group that will only contain this particular user, you can name it however you like.
6. Add the user to this group by clicking on the Add Members button on the right.
7. Go to  > General Configuration, Under Users & Security go to Global Permissions and click on Edit Permissions.
8. In the Groups section, add your newly created group, make sure it has the can use checkbox checked, and Save the changes.
9. Go back to Confluence administration and in the Space Permissions, make sure that the group you created is not listed in the Default Space Permissions.
10. On the same page, locate the space you wish to grant this user access to and click on Manage Permissions. This will lead you to the space permissions page.
11. Click on the Edit Permissions button below the list of groups.
12. In the text box, enter the name of the group you created and click Add.
13. Set the correct permissions you wish this group to have then click on Save All at the bottom of the page.

After completing these steps, your user will now be able to see and access only the desired space along with the Confluence main page.