In Jira Server you could just use Basic Auth.
- click F12 on your keyboard => Console
type in :
btoa("your-username:yourpassword")
A token should be generated, You can use it to authenticate with Postman or any other API Tool you might use.
Headers: "Authorization : Basic ${token}"
Jira cloud behaves different,
Creating PATs in application
In your Atlassian application go to:
In Confluence, select your profile picture at top right of the screen, then choose Settings > Personal Access Tokens .
In Jira, select your profile picture at the top right of the screen, then choose Profile.
Once you access your profile,
select Personal Access Tokens in the left-hand menu.
Select Create token.
Give your new token a name.
Optionally, for security reasons, you can set your token to automatically expire after a set number of days.