URL validator rejects valid upstream URLs

[rwos]

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Describe the bug

Upstream URLs of the form http://tasks.foo-bar_baz (and possibly others) are rejected as invalid, while they are perfectly valid. This is one of the forms Docker Swarm's internal DNS hostnames take (service baz in the stack foo-bar).

Reproducing the bug

1. Set upstream.url to http://tasks.foo-bar_baz

Relevant log output

time=2022-02-22T10:37:26Z level=error msg=A Rule uses a malformed configuration and all URLs matching this rule will not work. You should resolve this issue now. audience=application error=map[debug: message:An internal server error occurred, please contact the system administrator reason:Value "http://tasks.foo-bar_baz" of "upstream.url" is not a valid url. status:Internal Server Error status_code:500] rule_id=ory:foo:protected-bar service_name=ORY Oathkeeper service_version=v0.38.19-beta.1-17-g74c2581

Relevant configuration

No response

Version

v0.38.19-beta.1-17-g74c2581

On which operating system are you observing this issue?

Linux

In which environment are you deploying?

Docker

Additional Context

No response