add gitlab section

docs/Advanced/Gitlab.md

@@ -0,0 +1,61 @@
+---
+sort: 6
+title: Gitlab
+---
+
+```note
+There is a *self-hosted* **Gitlab** instance at **Gravity**
+    ```http
+    https://git.gravity.sjtu.edu.cn
+    ```
+```
+
+## Login
+
+[Open Gitlab on browser](https://git.gravity.sjtu.edu.cn/), there are **two ways** to login:
+
+1. Your *Gravity* username and password
+   ![Gitlab password login](../images/Advanced/gitlab-passwd-login.png)
+2. Use *Authelia* authorization at bottom of login page
+   ![Gitlab authelia login](../images/Advanced/gitlab-authelia-login.png)
+   ![Gitlab authelia confirm](../images/Advanced/gitlab-authelia-confirm.png)
+
+## SSH Access
+
+Like *Github*, you can use SSH to access *Gitlab*. But you need to add your SSH key to *Gitlab* first.
+
+Generate SSH key:
+
+```bash
+ssh-keygen -t rsa -b 4096 -C "$NAME@Gravity-Gitlab" -f /home/$NAME/.ssh/id_rsa_gitlab -q -N ""
+```
+
+You will generate two files: `~/.ssh/id_rsa_gitlab, ~/.ssh/id_rsa_gitlab.pub`. Copy your *public key* content to *Gitlab*:
+
+```bash
+~>  cat ~/.ssh/id_rsa_gitlab.pub
+
+# Output 👇
+ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQCcjFKepF608tQHKbrBJWSrUapb/cqFqJUNbCpqQT5UTzCY2j5CjlpNdxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxg3eHlDAVaM5nlP2Rk+z+7CG0lzcpH7BERKIQ== lalala@Gravity-Gitlab
+```
+
+Click account preferences on top right corner, then click **SSH Keys** on left sidebar, paste your public key to **Key** field, and click **Add key** button:
+![gitlab add SSH key](../images/Advanced/gitlab-add-ssh-key.png)
+
+Last step, we need to configure SSH to use this key. Add following content to `~/.ssh/config`:
+
+```bash
+Host git.gravity.sjtu.edu.cn
+    HostName git.gravity.sjtu.edu.cn
+    Port 33
+    IdentityFile ~/.ssh/id_rsa_gitlab
+```
+
+Let us try to access *Gitlab* now:
+
+```bash
+~> ssh -T git@git.gravity.sjtu.edu.cn
+
+# Output 👇
+Welcome to GitLab, @lalala!
+```