Cannot push to repository - Permission denied

How to Use GitLab System Administration
1

I cannot push to any repository although my SSH key is registered on the GitLab server.

$ git push -u origin master
git@gitlab.centos6-server.local's password: 
Permission denied, please try again.
git@gitlab.centos6-server.local's password: 
Permission denied, please try again.
git@gitlab.centos6-server.local's password: 
Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
fatal: The remote end hung up unexpectedly

Here is the configuration of GitLab instance:

System information
System:		CentOS 6.10
Current User:	git
Using RVM:	no
Ruby Version:	2.7.2p137
Gem Version:	3.1.4
Bundler Version:2.1.4
Rake Version:	13.0.1
Redis Version:	5.0.9
Git Version:	2.29.0
Sidekiq Version:5.2.9
Go Version:	unknown

GitLab information
Version:	13.6.7
Revision:	4d1fc8bce72
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	PostgreSQL
DB Version:	11.10
URL:		http://gitlab.centos6-server.local
HTTP Clone URL:	http://gitlab.centos6-server.local/some-group/some-project.git
SSH Clone URL:	git@gitlab.centos6-server.local:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers: 

GitLab Shell
Version:	13.13.1
Repository storage paths:
- default: 	/var/opt/gitlab/git-data/repositories
GitLab Shell path:		/opt/gitlab/embedded/service/gitlab-shell
Git:		/opt/gitlab/embedded/bin/git
2

I figured out the issue.

After adding the following lines to /etc/ssh/ssh_config and adding the user git to AllowUsers list in /etc/ssh/sshd_config, it no longer prompts for a password:

Host gitlab.centos6-server.local 
        RSAAuthentication yes 
        Preferredauthentications publickey 
        IdentityFile ~/.ssh/id_rsa
3

I figured out the issue.

After adding the following lines to /etc/ssh/ssh_config and adding the user git to AllowUsers list in /etc/ssh/sshd_config, it no longer prompts for a password:

Host gitlab.centos6-server.local 
        RSAAuthentication yes 
        Preferredauthentications publickey 
        IdentityFile ~/.ssh/id_rsa