Enable Custom HTTP client for communication with supertokens core

[jonathanmyers]

Environments like google cloud run require authentication for private service to service communication. This is currently difficult to accommodate between the sdk and supertokens core since there are no direct means of changing that client behavior.

Enabling some customization would help deployments in cloud run as well as other similar environments.

Workarounds include

• Making the supertokens core endpoint public
• Doing some network indirection using serverless vpc access and a load balancer
• Using runsd to proxy outbound requests and add the necessary headers

[rishabhpoddar]

hey @jonathanmyers thanks for this issue. It's not a priority for us at the moment, especially given that there are workarounds that you mentioned.

But feel free to make a PR for this :) Thanks