Squash & Merge Implementation

Hello, I'm trying to manually implement Github's *Squash&Merge *functionality. After looking many forums like stackoverflow.com I'm still struggling with the issue.

*The scenario is as follows*:
- master is a protected branch (configured on github)
- a service user *svc *is permitted to push to master (configured on github)
- other users don't have such permissions
- github PR status check is set to SUCCESS before execution of any set of
git commands below

1. This merges successfully without squash:
git checkout origin/master
git merge ${PR-Branch}
git push origin HEAD:master
git push origin --delete ${PR-Branch}

2. This closes the PR, but there is no update seen on master:
git checkout origin/master
git merge --squash --commit ${PR-Branch}
git push origin HEAD:master
git push origin --delete ${PR-Branch}

3. This fails to push to master with the error "GH006: Protected branch
update failed"  (despite that the PR is set to SUCCESS):
git checkout origin/master
git merge --squash ${PR-Branch}
git commit -am"comment"
git push origin HEAD:${m_mainBranch}
git push origin --delete ${m_prBranch}

Will appreciate your help on this.

Thanks, Vadim