Feature: Security audit logging with admin web query page

Add a dedicated security audit trail to the Go server. Login attempts,
authorization denials, WebSocket lifecycle, remote screen and terminal
sessions, clipboard operations, device authentication and admin mutations
now emit stable JSON-line events (audit=true, event=<name>) to a separate
logs/audit.log, mirrored to server.log. The path is configurable through
YAMA_AUDIT_LOG and the separate file can be switched off. Records never
contain passcodes, password hashes, tokens or clipboard contents, and
untrusted string fields are stripped of control characters and truncated
so they cannot forge log lines.

Expose the trail to administrators through a query_audit WebSocket command
and an Audit Log page in the web UI. The page filters by time range, event
(exact or prefix), actor, IP, device id, keyword and warning level, pages
newest-first, and stays hidden unless the server advertises the auditLog
capability, so older C++ servers degrade cleanly. Each query scans at most
the newest 32 MB of the current file to bound latency, records itself as
admin.audit.query, and tolerates torn or non-audit lines.

Add unit tests for event emission and redaction, query filtering, paging,
malformed lines, missing or disabled audit files, and handler
authorization.

Co-Authored-By: deepseek-flash

server/go/web/sso.go

@@ -33,26 +33,47 @@ func (s *Server) handleSSO(w http.ResponseWriter, r *http.Request) {
 	}
 	username, role, ok := s.sso.Detect(r)
 	if !ok {
+		// No usable portal credential: the normal fallback to the login form.
+		// Not audited — portal users without YAMA access hit this routinely.
 		s.unauthorized(w)
 		return
 	}
 	// Only the "admin" role may skip the login form via SSO. Every other role
 	// (viewer, unknown) must authenticate against YAMA's own login, even with
-	// a valid portal session.
+	// a valid portal session. A valid portal identity being refused here is
+	// worth an audit record: it is an authorization decision, not a login-form
+	// fallback.
 	if role != "admin" {
+		fields := requestFields(r, s.trustForwardedFor)
+		fields["method"] = "sso"
+		fields["actor"] = username
+		fields["role"] = role
+		fields["reason"] = "role_not_allowed"
+		s.log.AuditWarn(auditLoginFail, fields)
 		s.unauthorized(w)
 		return
 	}
 
 	token, err := s.auth.IssueToken(username, role)
 	if err != nil {
+		fields := requestFields(r, s.trustForwardedFor)
+		fields["method"] = "sso"
+		fields["actor"] = username
+		fields["role"] = role
+		fields["reason"] = "token_issue_failed"
+		fields["error"] = err.Error()
+		s.log.AuditWarn(auditLoginFail, fields)
 		w.Header().Set("Content-Type", "application/json")
 		w.WriteHeader(http.StatusInternalServerError)
 		_, _ = w.Write([]byte(`{"error":"internal error"}`))
 		return
 	}
 
-	s.log.Info("sso: user=%s role=%s", username, role)
+	fields := requestFields(r, s.trustForwardedFor)
+	fields["method"] = "sso"
+	fields["actor"] = username
+	fields["role"] = role
+	s.log.Audit(auditLoginOK, fields)
 	w.Header().Set("Content-Type", "application/json; charset=utf-8")
 	w.Header().Set("Cache-Control", "no-store")
 	_ = json.NewEncoder(w).Encode(map[string]string{