mcp-bash

#!/usr/bin/env bash # Remote authentication guard for proxied deployments. set -euo pipefail : "${MCPBASH_REMOTE_TOKEN_EXPECTED:=}" : "${MCPBASH_REMOTE_TOKEN_KEY:=}" : "${MCPBASH_REMOTE_TOKEN_FALLBACK_KEY:=}" : "${MCPBASH_REMOTE_TOKEN_ENABLED:=false}" : "${MCPBASH_REMOTE_TOKEN_DEBUG_WARNED:=false}" mcp_auth_rate_limit_failures() { if [ -z "${MCPBASH_STATE_DIR:-}" ]; then return 0 fi if [ "${MCPBASH_REMOTE_TOKEN_ENABLED:-false}" != "true" ]; then return 0 fi local max_fail="${MCPBASH_REMOTE_TOKEN_MAX_FAILURES_PER_MIN:-10}" case "${max_fail}" in '' | *[!0-9]*) max_fail=10 ;; 0) return 0 ;; esac local file="${MCPBASH_STATE_DIR}/auth.remote_token.fail.log" local lock_name="auth.remote_token.fail" local now local preserved="" local count=0 local line mcp_lock_acquire "${lock_name}" now="$(date +%s)" if [ -f "${file}" ]; then while IFS= read -r line; do [ -z "${line}" ] && continue if [ $((now - line)) -lt 60 ]; then preserved="${preserved}${line}"$'\n' count=$((count + 1)) fi done <"${file}" fi if [ "${count}" -ge "${max_fail}" ]; then printf '%s' "${preserved}" >"${file}" mcp_lock_release "${lock_name}" return 1 fi printf '%s%s\n' "${preserved}" "${now}" >"${file}" mcp_lock_release "${lock_name}" return 0 } mcp_auth_init() { local token="${MCPBASH_REMOTE_TOKEN:-}" local key="${MCPBASH_REMOTE_TOKEN_KEY:-mcpbash/remoteToken}" local fallback="${MCPBASH_REMOTE_TOKEN_FALLBACK_KEY:-remoteToken}" if [ -z "${token}" ]; then MCPBASH_REMOTE_TOKEN_ENABLED=false return 0 fi if [ "${MCPBASH_JSON_TOOL:-none}" = "none" ] || [ -z "${MCPBASH_JSON_TOOL_BIN:-}" ]; then printf '%s\n' "mcp-bash: MCPBASH_REMOTE_TOKEN is set but JSON tooling is unavailable; cannot enforce remote token guard." >&2 return 1 fi if [ -z "${key}" ]; then key="mcpbash/remoteToken" fi if [ "${#token}" -lt 32 ]; then printf '%s\n' "mcp-bash: MCPBASH_REMOTE_TOKEN must be at least 32 characters; refusing weak shared secret." >&2 return 1 fi MCPBASH_REMOTE_TOKEN_EXPECTED="${token}" MCPBASH_REMOTE_TOKEN_KEY="${key}" MCPBASH_REMOTE_TOKEN_FALLBACK_KEY="${fallback}" MCPBASH_REMOTE_TOKEN_ENABLED=true if [ "${MCPBASH_DEBUG_PAYLOADS:-false}" = "true" ] && [ "${MCPBASH_REMOTE_TOKEN_DEBUG_WARNED}" != "true" ]; then MCPBASH_REMOTE_TOKEN_DEBUG_WARNED="true" if mcp_runtime_log_allowed; then printf '%s\n' "mcp-bash: payload debug logging is enabled; remote tokens will be redacted in debug logs but disable debug in production." >&2 fi fi return 0 } mcp_auth_is_enabled() { [ "${MCPBASH_REMOTE_TOKEN_ENABLED:-false}" = "true" ] } mcp_auth_constant_time_equals() { local expected="$1" local provided="$2" local expected_len=${#expected} local provided_len=${#provided} local diff=$((expected_len ^ provided_len)) local max_len="${expected_len}" local i=0 if [ "${provided_len}" -gt "${max_len}" ]; then max_len="${provided_len}" fi while [ "${i}" -lt "${max_len}" ]; do local e=0 p=0 if [ "${i}" -lt "${expected_len}" ]; then LC_ALL=C printf -v e '%d' "'${expected:i:1}" fi if [ "${i}" -lt "${provided_len}" ]; then LC_ALL=C printf -v p '%d' "'${provided:i:1}" fi diff=$((diff | (e ^ p))) i=$((i + 1)) done [ "${diff}" -eq 0 ] } mcp_auth_extract_remote_token() { local json_line="$1" local key="${MCPBASH_REMOTE_TOKEN_KEY:-mcpbash/remoteToken}" local fallback="${MCPBASH_REMOTE_TOKEN_FALLBACK_KEY:-remoteToken}" local value="" value="$( { printf '%s' "${json_line}" | "${MCPBASH_JSON_TOOL_BIN}" -r --arg key "${key}" --arg fallback "${fallback}" ' def grab($k): ((.params._meta // {})[$k]? // empty | strings); (grab($key) // (if $fallback != "" then grab($fallback) else "" end)) '; } 2>/dev/null )" printf '%s' "${value}" } mcp_auth_emit_error() { local id_json="$1" local message="$2" # Notifications must not receive responses; skip when id is absent. case "${id_json}" in null | '') return 0 ;; esac rpc_send_line "$(mcp_core_build_error_response "${id_json}" -32602 "${message}" "")" } mcp_auth_guard_request() { local json_line="$1" local method="$2" local id_json="$3" if ! mcp_auth_is_enabled; then return 0 fi local presented presented="$(mcp_auth_extract_remote_token "${json_line}")" if [ -z "${presented}" ] || ! mcp_auth_constant_time_equals "${MCPBASH_REMOTE_TOKEN_EXPECTED}" "${presented}"; then if mcp_auth_rate_limit_failures; then if mcp_logging_is_enabled "warning"; then mcp_logging_warning "mcp.auth" "Remote token rejected method=${method}" fi mcp_auth_emit_error "${id_json:-null}" "Remote token missing or invalid" return 1 fi mcp_auth_emit_error "${id_json:-null}" "Remote token missing or invalid (throttled)" return 1 fi return 0 }