Go to your 'Setting' -> 'Personal Access Token' page, and generate an Access Token if you have not done that before. Copy and save the token to a safe place immediately as it will not show again.
Click 'Clone/Download' button in your repository view page, and copy the repository address from there.
Go to the console of your computer, paste the https git address, use your username and the access token to finish the git clone.
john$ git clone https://app.apigit.com/apigit/demo.git
Cloning into 'demo'...
Username for 'https://app.apigit.com': <<YOUR USER NAME HERE>>
Password for 'https://apigit@app.apigit.com': <<YOUR ACCESS TOKEN HERE>>
remote: Enumerating objects: 9, done.
remote: Counting objects: 100% (9/9), done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 9 (delta 0), reused 0 (delta 0), pack-reused 0
Unpacking objects: 100% (9/9), 2.09 KiB | 1.04 MiB/s, done.