This simplifies use cases where we intend to replace a manifest uniquely
identified by a set of labels with another one as is the case for
policies.
This helped fix annoying test flake on Windows where the clock is not
guaranteed to move forward when read in quick succession.
This is now passing on Windows:
```
$ go test -timeout 1000s ./internal/server -run TestSourceRefreshesAfterPolicy -count=1000
```
* nit: replaced harcoded string constants with named constants
* acl: added management of ACL entries
* auth: implemented DefaultAuthorizer which uses ACLs if any entries are found in the system and falls back to LegacyAuthorizer if not
* cli: switch to DefaultAuthorizer when starting server
* cli: added ACL management
* server: refactored authenticator + added refresh
Authenticator is now an interface which also supports Refresh.
* authz: refactored authorizer to be an interface + added Refresh()
* server: refresh authentication and authorizer
* e2e tests for ACLs
* server: handling of SIGHUP to refresh authn/authz caches
* server: reorganized flags to specify auth options:
- removed '--allow-repository-users' - it's always on
- one of --without-password, --server-password or --random-password
can be specified to specify password for the UI user
- htpasswd-file - can be specified to provide password for UI or remote
users
* cli: moved 'kopia user' to 'kopia server user'
* server: allow all UI actions if no authenticator is set
* acl: removed priority until we have a better understood use case for it
* acl: added validation of allowed labels when adding ACL entries
* site: added docs for ACLs
* Added draft release notes for 0.8
* Moved some content to 'advanced' section.
* Added conceptual documentation for actions, caching and logging.
* Updated site footer.
* user: validate that usernames in repository are all-lowercase and user@hostname-without-domain
* user: relaxed validation to allow -, _ and . in username and hostname
* user: added user profile (username&password for authentication) and CRUD methods
* manifest: helpers for disambiguating manifest entries
* authn: added repository-based user authenticator
* cli: added commands to manipulate user accounts and passwords
* cli: added --allow-repository-users option to 'server start'
* Update cli/command_user_info.go
Co-authored-by: Julio López <julio+gh@kasten.io>
* Always return false when the user is not found.
