If external auth is used, remove `/register` items from header nav.

(logic moved from docker-image settings file)

services/web/app/coffee/infrastructure/ExpressLocals.coffee

@@ -244,6 +244,17 @@ module.exports = (app, webRouter, apiRouter)->
 		for key, value of Settings.nav
 			res.locals.nav[key] = _.clone(Settings.nav[key])
 		res.locals.templates = Settings.templateLinks
+		try
+			externalAuth = res.locals.externalAuthenticationSystemUsed()
+			if externalAuth and res.locals.nav.header?
+				# filter out '/register' link
+				res.locals.nav.header = _.filter(
+					res.locals.nav.header,
+					(h) ->
+						h.url != '/register'
+				)
+		catch error
+			logger.error {error}, "error while trying to filter out '/register' links from header"
 		next()
 
 	webRouter.use (req, res, next) ->