Azure Pipelines: I am getting fatal: could not read Username for 'https://github.com': terminal prompts disabled

There is a built-in "service account" which is actually a PAT called Project Collection Build Service, not to be confused with Project Collection Build Service Accounts group.

From: https://marcstan.net/blog/2018/08/31/Mirror-github-gitlab-and-VSTS-repositories/

Trivia: In case you didn't know "$env:SYSTEM_ACCESSTOKEN" is a PAT (Personal/Private Access Token) that is auto generated by the build server (but disabled by default) and allows to authenticate against VSTS from inside your builds and releases. To enable it, you have select the "agent job" inside your build or release definition and check the "Allow scripts to access the OAuth token" checkbox under "Additional options".

There are two steps to this:

Step 1

To get rid of the fatal: could not read username for... error, we need to allow scripts to access the OAuth token. If you're using the newest YAML-based Azure Pipeline, you'll be hunting high and low for "Allow scripts to access the OAuth token" option in the UI. The Microsoft answer is here. In your YAML file (azure-pipelines.yml), add:

steps:
- checkout: self
  persistCredentials: true

Step 2

After resolving the OP's error, I couldn't commit, receiving the error:

remote: 001f# service=git-receive-pack
remote: 0000000000aaTF401027: You need the Git 'GenericContribute' permission to perform this action. Details: identity 'Build\c21ba3ac-5ad4-de50-bc1a-12ee21de21f0', scope 'repository'.
remote: TF401027: You need the Git 'GenericContribute' permission to perform this action. Details: identity 'Build\c21ba3ac-5ad4-de50-bc1a-12ee21de21f0', scope 'repository'.
fatal: unable to access 'https://[username].visualstudio.com/[repo]/_git/[repo]/': The requested URL returned error: 403

We also have to give it permissions. From the same page as above. Add the user Project Collection Build Service to your repo(s).

Note: The user (1) and not the group (2).

Grant:

Contribute: Allow
Create Branch: Allow
Create Tag: Allow (Inherited)
Read: Allow (Inherited)

HTH

Not the exact same situation you have but this was the only post that came close to my similar situation so I thought it's worth adding my solution here. I had this error in a hosted Ubuntu Azure Pipeline, running a shell command task to checkout, edit and push to git.

I got the error when attempting to push with command:

git push

I fixed it by changing the command to:

git -c http.extraheader="AUTHORIZATION: bearer $(System.AccessToken)" push

$(System.AccessToken) is a predefined variable in the Azure Pipelines: https://docs.microsoft.com/en-us/azure/devops/pipelines/build/variables?view=azure-devops&viewFallbackFrom=vsts&tabs=yaml