Express JS proxy to call web api

You can get the URL to be proxied as a query parameter, modify it and then pass that URL to proxy, like this (use instead of app.use('/proxy', proxy('http://localhost:56660/api/values'));):

app.get('/proxy', (req, res, next) => {    const modifiedURL = modifyURL(req.query.url)    return proxy(modifiedURL)(req, res, next)})

You can call you server with an URL like this (GET method):

https://my.server.com/proxy?url=https://urltobeproxied.com

UPDATE:

I think this would work according to your needs:

app.use('/proxy', (req, res, next) => {    const requestedUrl = `${req.protocol}://${req.get('Host')}${req.url}`    const modifiedURL = modifyURL(requestedUrl)    proxy(modifiedURL)(req, res, next)})

UPDATE2:

app.use('/proxy', proxy('http://localhost:56660/api/values', {  proxyReqPathResolver: function(req) {    const requestedUrl = `${req.protocol}://${req.get('Host')}${req.url}`    const modifiedURL = modifyURL(requestedUrl)    return require('url').parse(modifiedURL).path;  }}))

UPDATE3:

An example of proxy modifying the response (extracted from the package docs);

app.use('/proxy', proxy('http://localhost:56660/api/values', {  userResDecorator: function(proxyRes, proxyResData, userReq, userRes) {    data = JSON.parse(proxyResData.toString('utf8'));    data.newProperty = 'exciting data';    return JSON.stringify(data);  }}))