For Azure DevOps Service Connections you need personal access tokens to provide granular permissions, also if you are a consultant, you don’t want your account to get mapped into the customers service connection. it would be a decent way to keeping the tokens within the organization connections.
Go to your GitHub organization profile or your repo profile.
New Fine-grained Personal Access Token (github.com)
Choose specific Repo. –
Added repo permissions for the token
now you can use this access token in the azure DevOps service connection.