nginx - direct multiple subdomain to directory of subdomain name

I would like to direct multiple (but specific) subdomains in a single server block to a path of the same name, using proxy_pass:

api.example.com to www.example.com/api webhook.example.com to www.example.com/webhook iframe.example.com to www.example.com.webook

This directs all requests from api, webhook, and iframe to /api, but I would like to direct api to /api, webhook to /webhook etc.

server {
    listen 443 ssl http2;

    #tls/ssl certificates
    ssl_certificate /etc/ssl/example.crt;
    ssl_certificate_key /etc/ssl/example.key;

    #specify subdomains
    server_name api.example.com webhook.example.com iframe.example.com;

    #reverse proxy to localhost
    location / {
        proxy_pass https://127.0.0.1/api$request_uri;
        proxy_set_header Host "www.example.com";
    }
}

Is it possible to specify the primary directory as a function of the subdomain, or does this need to be three separate server blocks?