API user accounts and regular user accounts all use the SystemWeaver Client API to connect to the server, and are all handled in the same way. That is, accounts that will be used for API applications are also created and maintained using the swAdmin2 client, and each usage is required to have its own login credentials.
Accounts using the SystemWeaver API can be read-only or read/write. Just like with regular accounts, when you create the account, you can assign the "Viewer" role to it and it will be limited to read-only for items. However, note that the "Viewer" roll does not limit the account using the SystemWeaver API to read-only for Issues if you give the account access to a CMS Project.