Add transaction signing example code in java

[Kartiiyer12]

Why

To make the repo have e2e testing and cover all the test cases, transaction signing should also be included.

What

We need to have a java based transaction signing code example similar to what we have in ts - https://github.com/cardano-foundation/cardano-rosetta/blob/master/examples/postman/sign-transaction-server.js

[Kammerlo]

Hey thanks for raising this.
Question, do you want to have an additional endpoint to sign transactions (like in the example you shared) or do you just want en e2e transaction signing written in java?

[Kartiiyer12]

The way it works currently is we can send a pre-request from the /combine endpoint where the the transaction is signed on another server endpoint(probably an internal cold server where keys exists) and the response from the /combine request is the signed transaction which can be submitted. So I think an separate api end point not within the rosetta api list.

What do you mean by e2e transaction signing? How would that integrate with rosetta API calls?

[Kammerlo]

We could add an additional endpoint e.g. /construction/sign with the same functionality. Then users are free to decide how to use it. In offline_mode in a cold environment or where ever they need it.

[Kartiiyer12]

Yeah, that would b e good custom addition to the endpoint.