logout-all.patch

diff --git a/nextstrain/cli/authn.py b/nextstrain/cli/authn.py
index 93515ce..6cd2af0 100644
--- a/nextstrain/cli/authn.py
+++ b/nextstrain/cli/authn.py
@@ -173,6 +173,26 @@ def logout(origin: Origin):
         print(f"Not logged in to {origin}.", file = stderr)
 
 
+def logout_all():
+    """
+    XXX FIXME
+    """
+    with config.write_lock():
+        secrets = config.load(config.SECRETS)
+
+        sections = [
+            (section, _parse_section(section))
+                for section in secrets
+                 if _parse_section(section) ]
+
+        for section, origin in sections:
+            del secrets[section]
+            print(f"Credentials for {origin} removed from {config.SECRETS}.", file = stderr)
+            print(f"Logged out of {origin}.", file = stderr)
+
+        config.save(secrets, config.SECRETS)
+
+
 def current_user(origin: Origin) -> Optional[User]:
     """
     Information about the currently logged in user for *origin*, if any.
@@ -257,3 +265,12 @@ def _config_section(origin: Origin) -> str:
     if origin == "https://nextstrain.org":
         return CONFIG_SECTION
     return f"{CONFIG_SECTION} {origin}"
+
+
+def _parse_section(section: str) -> Optional[Origin]:
+    if section == CONFIG_SECTION:
+        return Origin("https://nextstrain.org")
+    elif section.startswith(CONFIG_SECTION + " "):
+        return Origin(section.split(" ", 1)[1])
+    else:
+        return None