Disallow unauthenticated requests for privileged endpoints

[HalosGhost]

The mintTx endpoint is incredibly privileged operation. Right now, there's no restriction on interacting with that interface. This is unacceptable for a production-grade deployment.

Given the intended use-case this repository is exploring (unprivileged, non-custodied wallet providers), such an interface likely shouldn't/wouldn't actually exist in a productionized fork/recreation of this project. However, some variant of endpoint authentication would not go amiss, to make sure no one gets the wrong idea.

Originally posted by @anders94 in #6 (comment)

[HalosGhost]

Note: this also requires some level of authentication to be present in the running equivalent of opencbdc-tx because authentication of privileged operations should be strict and verified (at least) at the boundaries of the security perimeter (which this repository sits outside).

cf. mit-dci/opencbdc-tx#98

[anders94]

This might be duplicated in #7 and #8

[HalosGhost]

closing as a duplicate of already-open issues.