cli: --offline means fully offline

With this change, `--offline` also disables TUF
repository updates and not just online log lookups.

Closes #483.

Signed-off-by: William Woodruff <william@trailofbits.com>

sigstore/_cli.py

@@ -996,12 +996,12 @@ def _collect_verification_state(
 
     if args.staging:
         _logger.debug("verify: staging instances requested")
-        verifier = Verifier.staging()
+        verifier = Verifier.staging(offline=args.offline)
     elif args.trust_config:
         trust_config = ClientTrustConfig.from_json(args.trust_config.read_text())
         verifier = Verifier._from_trust_config(trust_config)
     else:
-        verifier = Verifier.production()
+        verifier = Verifier.production(offline=args.offline)
 
     all_materials = []
     for file_or_hashed, materials in input_map.items():

sigstore/verify/verifier.py

@@ -77,23 +77,23 @@ def __init__(self, *, rekor: RekorClient, trusted_root: TrustedRoot):
         self._trusted_root = trusted_root
 
     @classmethod
-    def production(cls) -> Verifier:
+    def production(cls, *, offline: bool = False) -> Verifier:
         """
         Return a `Verifier` instance configured against Sigstore's production-level services.
         """
         return cls(
             rekor=RekorClient.production(),
-            trusted_root=TrustedRoot.production(),
+            trusted_root=TrustedRoot.production(offline=offline),
         )
 
     @classmethod
-    def staging(cls) -> Verifier:
+    def staging(cls, *, offline: bool = False) -> Verifier:
         """
         Return a `Verifier` instance configured against Sigstore's staging-level services.
         """
         return cls(
             rekor=RekorClient.staging(),
-            trusted_root=TrustedRoot.staging(),
+            trusted_root=TrustedRoot.staging(offline=offline),
         )
 
     @classmethod