Regex to match JWT

Question

I don't have experience with Regex and I'm asking for your help.

I need a regex to capture the JWT inside the following string:

"contextJwt": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJIZWxsbyB5b3UiLCJuYW1lIjoiV2h5IGFyZSB5b3UgY2hlY2tpbmcgbXkgdG9rZW4_ICggzaHCsCDNnMqWIM2hwrApIiwiaWF0IjoxNTE2MjM5MDIyfQ.yAP0xiTwp6vqIYbLKLVBRv-gTyMvU17rT3H8uErLjHA"

Request answer (2363 lines)

Thanks for your time

Answer 1

If you are working with an HTML document as a string and you are using Javascript to run your regular expression, you could do something like the following:

const html = '<div>stuff</div>something "contextJwt": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJIZWxsbyB5b3UiLCJuYW1lIjoiV2h5IGFyZSB5b3UgY2hlY2tpbmcgbXkgdG9rZW4_ICggzaHCsCDNnMqWIM2hwrApIiwiaWF0IjoxNTE2MjM5MDIyfQ.yAP0xiTwp6vqIYbLKLVBRv-gTyMvU17rT3H8uErLjHA" <div> other stuff</div>';
var regex = /"contextJwt":\s*"(.*)"/;
console.log(html.match(regex)[1]);

/* yields the encoded JWT string:
 eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJIZWxsbyB5b3UiLCJuYW1lIjoiV2h5IGFyZSB5b3UgY2hlY2tpbmcgbXkgdG9rZW4_ICggzaHCsCDNnMqWIM2hwrApIiwiaWF0IjoxNTE2MjM5MDIyfQ.yAP0xiTwp6vqIYbLKLVBRv-gTyMvU17rT3H8uErLjHA

*/

You can tighten up your match from the simple (.*) to the specific characters that are allowed in a valid encoded JWT (per Helio Santo's answer), but since regexes are finicky, I usually start with the simplest solution and only tighten it down when necessary.

What you do with the string that represents an encoded JWT is perhaps another question entirely.