adding a command line argument to print hook output as json

[eddiez9]

Problem
I'd like to alert off newly added secrets using detect-secrets-hook and a baseline file in a pipeline job.

Currently using the following command results in pretty printed text. This is difficult to parse programattically.

git ls-files -z | xargs -0 detect-secrets-hook --baseline .secrets.baseline

ERROR: Potential secrets about to be committed to git repo!

Secret Type: Secret Keyword
Location:    src/blah/appsettings.Development.json:41

Possible mitigations:
  - For information about putting your secrets in a safer place, please ask in
    #security
  - Mark false positives with an inline `pragma: allowlist secret`
    comment

Solution
Added a command line argument to print the newsecrets output as JSON the same way the baseline files are made so I can parse it for the results object.

git ls-files -z | detect-secrets-hook --json --baseline .secrets.baseline

...
"results": {
    "src/blah/appsettings.Development.json": [
      {
        "type": "Secret Keyword",
        "filename": "src/blah/appsettings.Development.json",
        "hashed_secret": "7fa361e59adef2ea0b8571032025a433f926124a",
        "is_verified": false,
        "line_number": 41
      }
    ]
  },
...

[eddiez9]

Hey there, requesting any feedback on this PR
@lorenzodb1 @jpdakran

[jpdakran]

Thanks for your contribution. LGTM 👍 . Can you update this section of the README with the new argument? https://github.com/Yelp/detect-secrets#blocking-secrets-not-in-baseline Thanks!

[eddiez9]

Thanks!

Have updated the readme with the new argument

[jpdakran]

LGTM 👍 Thank you for your contribution.

[jpdakran]

I forgot to ask. Do you mind adding some unit tests for this? @eddiez9

[eddiez9]

Was going to add some but I see you've already done so!