pebble - 2.4.0+ds1-2+b4 main

Pebble is a miniature version of Boulder
(https://github.com/letsencrypt/boulder) that can assist in the
development and testing of ACME clients against the standard without
having to setup a full production-capable ACME server.
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Pebble is NOT designed for production use and is for testing only. By
design, it will drop all of its state between invocations and will
randomize keys and certificates used for issuance!
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Pebble has several top level goals:
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1. Provide a simplified ACME testing front end
2. Provide a test-bed for new and compatibility breaking ACME features
3. Encourage ACME client best-practices
4. Aggressively build in guardrails against non-testing usage