Jenkins git checkout "Authentication failed" over HTTPS in CI

Git reached the HTTPS remote but the credentials were rejected. The username/password or token Jenkins supplied is missing, wrong, expired, or has no access to the repository, so the clone is denied.

What this error means

The checkout fails with remote: Invalid username or password (or token) and fatal: Authentication failed for 'https://git.example.com/org/repo.git/'.

Jenkins console

remote: Support for password authentication was removed.
fatal: Authentication failed for 'https://github.com/org/repo.git/'

Common causes

Missing or wrong credentials binding

The job references no credential, or the wrong credential ID, so git sends no valid secret to the HTTPS remote.

An expired or unscoped token

A personal access token expired or lacks repo read scope; many hosts no longer accept account passwords, only tokens.

How to fix it

Attach a valid token credential

Create a "Username with password" credential whose password is a valid PAT with repo read scope.
Select that credential in the job's SCM / checkout step.
Rotate the token if it expired and update the credential in one place.

Jenkinsfile

checkout scmGit(
  userRemoteConfigs: [[url: 'https://github.com/org/repo.git',
                       credentialsId: 'github-pat']],
  branches: [[name: '*/main']])

How to prevent it

Use token-based credentials; many hosts reject passwords.
Track token expiry and rotate before it lapses.
Grant least-privilege repo read scope to CI tokens.