How do we validate the format of the CSR using Regex

I'm currently trying to validate a CSRformat via javascript regex and I'm currently stuck with this regex:

^ (-----BEGIN NEW CERTIFICATE REQUEST-----)(.*[\r\ n]) + (-----END NEW CERTIFICATE REQUEST-----) $

What I want to accomplish is that I need to validate only the 1st occurence of the

-----BEGIN NEW CERTIFICATE REQUEST-----

and

-----END NEW CERTIFICATE REQUEST-----

so anything below except white spaces or enter spaces becomes invalid.

This must be invalid as well:

    -----BEGIN NEW CERTIFICATE REQUEST-----
test
test
test
test
    -----END NEW CERTIFICATE REQUEST-----
    -----BEGIN NEW CERTIFICATE REQUEST-----
test
test
test
test
    -----END NEW CERTIFICATE REQUEST-----

it should only be:

    -----BEGIN NEW CERTIFICATE REQUEST-----
test
test
test
test
    -----END NEW CERTIFICATE REQUEST-----

Looks like I'm getting a hard time as well to figure this out via RegEx

Solution

You can use this version of regex that will capture only the first START/END block only in case it is a unique block of this kind:

^(?:(?!-{3,}(?:BEGIN|END) NEW CERTIFICATE REQUEST)[\s\S])*(-{3,}BEGIN NEW CERTIFICATE REQUEST(?:(?!-{3,}END NEW CERTIFICATE REQUEST)[\s\S])*?-{3,}END NEW CERTIFICATE REQUEST-{3,})(?![\s\S]*?-{3,}BEGIN NEW CERTIFICATE REQUEST[\s\S]+?-{3,}END NEW CERTIFICATE REQUEST[\s\S]*?$)

See demo

EDIT:

To make sure we just match at the end, with optional spaces, you can use a shorter regex:

^(?:(?!-{3,}(?:BEGIN|END) NEW CERTIFICATE REQUEST)[\s\S])*(-{3,}BEGIN NEW CERTIFICATE REQUEST(?:(?!-{3,}BEGIN NEW CERTIFICATE REQUEST)[\s\S])*?-{3,}END NEW CERTIFICATE REQUEST-{3,})\s*$

See Demo 2