When you are working with a trusted developer, the normal procedure is to add them to your Development Team on App Store Connect (Users and Access).
You assign them an appropriate role (depending on what you want them to do), which might be (for example):
• Developer (for development)
• App Manager (for distribution)
The role allows the developer to do what they need to do, and no more.
For example, no access to your accounts!
With an untrusted developer, then things are much harder.
You either need to do things yourself, or find someone that you do trust, and get them to do it!
On Users and Access, you can see the exact "Permissions" that each role has (for the apps you have assigned to them), to help you decide which to use.
More information here:
https://developer.apple.com/support/roles/
Topic:
Code Signing
SubTopic:
Certificates, Identifiers & Profiles
Tags: