There have been a handful of web based clients in the past.
ISRG / LetsEncrypt officially recommends against Web Based Clients due to concerns over Security and User Experience - most notably the likelihood of missed renewals. Web Based Clients have been actively removed from the LetsEncrypt website. LetsEncrypt actively recommends against third party Web Based Clients, and their comments on the matter apply almost equally to a potential first party Web Based Client.
It's not going to happen.
See: