Add webhook/trigger events

[cumuru]

To reduce server load and increase responsiveness I suggest to add two things:

1. a webhook endpoint for triggering satis updates on single repositories (e.g. for Github)
2. an event triggered by satisfy that updates packages.json once a new repository is added (or removed or updated)

In depth:
1)

• Would be nice to support Github API (https://developer.github.com/webhooks/) and others?
• Should be secured by a secret token (https://developer.github.com/webhooks/securing/). The token should be configurable either in config file or via environment.
• Repository name in (Github) payload is different from satis and needs to be normalized (for SSH)

• An event should fire on every action that modifies the set of repositories. Might trigger a complete rebuild maybe (opinions?)

My goal is to have three ways of updating packages.json:

• A push webhook that rebuilds a single repo
• An event that rebuild a single repo or everything
• A cronjob that runs maybe once a day, just in case any change is missed by the above measures.

See #45.

[cumuru]

Some input for implementation:

• satis consumes (on CLI) a param --repository-url=ssh://[email protected]/pathto/repo.git to update a single repo only
• working Regex to normalize SSH repo uri (Github):
  preg_replace('/^(\w+@)?([\w\.]+)(:\d+)?:(.*)$/', 'ssh://$1$2$3/$4')
  ($1 = user, $2 = host, $3 = port, $4 = repository path)
• composer package dealing with Github API (signature validation and payload normalization): https://packagist.org/packages/swop/github-webhook
• One could iterate over satis.json‘s repositories to whitelist incoming push events.

[ramunasd]

Bitbucket webhook example:
mtomala@a10c1df

A lot of duplicated code, but principe on itself is clear.

[ramunasd]

Currently satis build with repository filter throws exception.
composer/satis#493

[ramunasd]

Implemented & tested against real VCS.