Not sure what you mean "secure telegraph into influxdb" but we've had great success with this stack for monitoring by just embedding an HTTP server into each application that needs to be monitored. We keep the HTTP server separate from any others used by the application (i.e. it runs on a separate thread) so performance isn't impacted.
My use case is one where I have servers in different datacenters and would want to have a simple, but secure, way to fetch metrics for graphing and alerts.
So, I meant encryption in transport, authentication, etc. as many solutions work well if you're monitoring "in the clear" from the backend, but not so much over the internet.
We're deployed on AWS in multiple regions with VPNs set up between VPCs. No particular attention paid to securing the transport between Telegraf and Influx at the moment since a) it's either in an internal VPC or secured via ipsec, and b) our monitoring data is low-value enough that it doesn't warrant its own secure transport.