I consistently got the exception below at the beginning of every build for several hours yesterday (2021-06-30).

Since the Git plugin only supports username + password (not secret text) credentials, I have added my GitHub personal access token as the "password" with a dummy "username" as instructed in the plugin instructions. The exception below was also shown in the UI below the dropdown where you can select a credential.

The error was no longer there this morning, after the GitHub brownout was over, but we can expect this to break as soon as GitHub permanently discontinues username + password auth, and it would be good to fixed soon.

hudson.plugins.git.GitException: Command "git fetch --tags --force --progress --prune – origin +refs/heads/develop:refs/remotes/origin/develop" returned status code 128:
stdout:
stderr: remote: Password authentication is temporarily disabled as part of a brownout. Please use a personal access token instead.
remote: Please see https://github.blog/2020-07-30-token-authentication-requirements-for-api-and-git-operations/ for more information.
fatal: unable to access 'https://github.com/***/**.git/': The requested URL returned error: 403

at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandIn(CliGitAPIImpl.java:2661)
at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.launchCommandWithCredentials(CliGitAPIImpl.java:2086)
at org.jenkinsci.plugins.gitclient.CliGitAPIImpl.access$500(CliGitAPIImpl.java:86)
at org.jenkinsci.plugins.gitclient.CliGitAPIImpl$1.execute(CliGitAPIImpl.java:608)
at jenkins.plugins.git.GitSCMFileSystem$BuilderImpl.build(GitSCMFileSystem.java:365)
at jenkins.scm.api.SCMFileSystem.of(SCMFileSystem.java:197)
at jenkins.scm.api.SCMFileSystem.of(SCMFileSystem.java:173)
at org.jenkinsci.plugins.workflow.cps.CpsScmFlowDefinition.create(CpsScmFlowDefinition.java:114)
at org.jenkinsci.plugins.workflow.cps.CpsScmFlowDefinition.create(CpsScmFlowDefinition.java:68)
at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:309)
at hudson.model.ResourceController.execute(ResourceController.java:97)
at hudson.model.Executor.run(Executor.java:429)
Finished: FAILURE