I was trying to get list of sub webs under a web. Initially I used https://companyname.com/_api/Web/Webs as I got webs I thought webinfos is a right candidate. But even then I get a access denied. 

More specifically, when read-only user access the page containing this REST endpoint, SharePoint opens up prompt asking credentials. Read-only user has access to all the webs.

Any idea what I am missing ? Is there a special permission I need to grant the user to view all the webs ?

Hi,

Per my knowledge, the read-only permission can't access the /_api/Web/WebInfos EndPoint. If you want to get the webs information we can use Search REST API to achieve it.

https://companyname.com/_api/search/query?querytext='path:https://companyname.com/*'&refinementfilters='contentclass:equals("STS_Web")'

Best Regards,

Dennis