Unable to fetch payload.access_token value after hitting salesforce using http connector. how to extract access_token value?

I am hitting salesforce which is giving me application/x-www-form-urlencoded JSON which looks like this

{"access_token":"00D5j0008yLhA!ARwAQBufl2Y6S1Tu3AU5zUWBCb442Nj2JqwWFOkm3AFL16CQZleLO.mnZwlDFttOMEnldbt_WqJBzhLrh1mgI1XEIvAN8sAM","instance_url":"https://cloudceitude-13a-dev-ed.my.salesforce.com","id":"https://login.salesforce.com/id/00D5j00000LhAEAU/0055j000004TZbAAAW","token_type":"Bearer","issued_at":"1668188564383","signature":"LQbWIODP8pqE+wD1yjgbVUBxMDI6YV1HjENZUeK/eoY="}

but when I am trying to access value of access_token using payload.access_token it is giving me error

I have tried by transforming into JSON using Transform connector using

%dw 2.0
output application/json
​---
payload

still after I tried to access my token it shows same error

and also while debugging map function is not working while working on Payload in DataWeave but instead when I use MapObject It reflect this:

key=%7B%22access_token%22%3A%2200D5j000008yLhA%21ARwAQIN5UGZWtk8Ucu8MUNgbnHAKleeqAk2M73Afy9iRKNEKRppu4C7Drfi0hg8q5t8C.PYX7RsMMXQPsjxmpVB1Ev_pU.2p%22%2C%22instance_url%22%3A%22https%3A%2F%2Fcloudcertitude-13a-dev-ed.my.salesforce.com%22%2C%22id%22%3A%22https%3A%2F%2Flogin.salesforce.com%2Fid%2F00D5j000008yLhAEAU%2F0055j000004TZbAAAW%22%2C%22token_type%22%3A%22Bearer%22%2C%22issued_at%22%3A%221668330168420%22%2C%22signature%22%3A%22kkDnnUe9pZfiqiuEjRi02az0lwpAlmwmv3cMRmF9nRU

I'll make an educated guess that the application or the server are somehow forcing the media type of the response to be application/x-www-form-urlencoded when it really is a JSON. The request for a token should be application/x-www-form-urlencoded, the response should be a JSON (application/json). If the server is returning it you should check with the administrators of that server. However if the application is overriding the content type of the response you should fix it.