Fine-tune SATP session with user input

[RafaelAPB]

Allow for user input at various stages of the SATP protocol. A user might want to cancel a transaction after submission due to several reasons (e.g., bad rate from counterparty gateway, which would be at the end of stage 0 / start of stage 1; or a bit later, e.g., right before lock, if bridge rate is bad);

Tasks:

1- Define a mechanism to allow for user input during different stages of SATP execution. 2- Test using functions that implement some kind of business rules in the middle of the execution of the protocol

[petermetz]

@RafaelAPB Quick question: Is this specified on the spec level as well? E.g. does the spec say that these user-driven hook points need to be implemented? Just curious.

[solo-daemon]

Hi @petermetz @RafaelAPB I would like to work on this issue. Could you please provide me a quick background to start from

[RafaelAPB]

@petermetz thanks for your question. The answer is no: the spec does not define that stages can be stopped and awaiting user input. But this will certainly be a need, since you could get for example a quote from the counterparty gateway that is too high. We should raise this in IETF.

@solo-daemon study the satp-dev branch, and let me know if you have any doubts (via Hyperledger discord, cacti channel)