Description of problem:

The new "secret reader script" does not produce a correct JSON document when the content of the secrets contain characters which are not valid in a JSON string like newlines or quotation marks.

Example configuration:

tls:
  ca:
    key: service-ca.crt
    secret:
      name: collector-manual-token 

(The "service-ca.crt" field of the secret contains a PEM-encoded TLS certificate which contains newlines)

Output of vector container:

2024-07-03T13:43:11.406275Z ERROR vector::cli: Configuration error. error=Error while retrieving secret from backend "from_secret": control character (\u0000-\u001F) found while parsing a string at line 3 column 0. 

Currently the script simply concatenates a JSON template string with the contents of the secret(s), which in this case produces invalid JSON. Ideally we have something that properly marshals a JSON document from the content, so that it is valid no matter what the content of the secrets is.

Version-Release number of selected component (if applicable):

6.0 (master)

How reproducible:

Create a ClusterLogForwarder referencing a secret that contains characters which are invalid inside a JSON string.

Actual results:

Vector fails to start up, because it can not parse the output from the secrets script.

Expected results:

Vector can read the secrets no matter what they contain and successfully start up.