Boundary between securesystemslib and TUF is off.

[awwad]

Some of the functions in securesystemslib are really pieces of TUF that I don't think are of use to others and don't belong here.

Some examples that IIUC don't belong in securesystemslib:

• util.ensure_all_targets_allowed(rolename, list_of_targets, parent_delegations)
• util.find_delegated_role(roles, delegated_role)
• formats.NUMBINS_SCHEMA
• formats.TARGETS_SCHEMA
• formats.SNAPSHOT_SCHEMA
• formats.TIMESTAMP_SCHEMA
• formats.ROOT_SCHEMA
• formats.MIRRORDICT_SCHEMA
• formats.MIRRORLIST_SCHEMA

Other functions that could conceivably be useful in general have zero context within the module:

• util.paths_are_consistent_with_hash_prefixes(paths, path_hash_prefixes)
• formats.PROJECT_CFG_SCHEMA

Things I'm less sure about:

• formats.THRESHOLD_SCHEMA
• exceptions.RoleAlreadyExistsError
• exceptions.UnknownRoleError
• formats.ROLENAME_SCHEMA

[JustinCappos]

The general concept makes sense to me.

[lukpueh]

We have some utility functions implemented in in-toto that might be a good fit for securesystemslib (see in-toto/in-toto#80).

[lukpueh]

IMHO #35 and #75 are also related to this issue.

[lukpueh]

Fixed with #165