Mapping from JWT Claims

Inject user or tenant claims into upstream requests after the gateway verifies the token. Any standard or custom JWT claim is available via

Inject user or tenant claims into upstream requests after the gateway verifies the token. Any standard or custom JWT claim is available via $request.jwt.<claim>. This lets your backend trust user identity without re-validating the token, since the gateway already verified it.

Last reviewed: 2026-03-06

When to use this

Use the mapping and variables reference when you need to transform, inject, or replace values in upstream requests. Mapping lets you forward selected headers, query parameters, JWT claims, and config variables to the upstream without modifying your backend code.

Key concepts

• The mapping block on a path entry defines which headers and query parameters to send to the upstream. Only mapped values are forwarded -- unmapped client headers and query params are dropped.

• Mapping sources include $request.headers.*, $request.query.*, $request.jwt.* (any JWT claim), $config.* (global variables), and $route.* (route-level variables).

• Global variables are defined at the top level of the config and available to all routes. Route-level variables are defined inside a path entry and override global variables with the same name.

• $env.* and $secrets.* placeholders are replaced at config load time, not at request time. This means environment variables and secrets are baked into the parsed config once at startup.

• If a mapping source resolves to null or undefined, the gateway sends an empty string for that header or query parameter. Use the debugging guide to trace missing values.

Repo-grounded example

{
  "variables": { "region": "eu-west-1" },
  "paths": [
    {
      "method": "GET",
      "path": "/proxy/{.+}",
      "auth": true,
      "integration": { "type": "http_proxy", "server": "upstream" },
      "mapping": {
        "headers": {
          "x-user-id": "$request.jwt.sub",
          "x-region": "$config.region"
        },
        "query": {
          "source": "$request.query.source"
        }
      },
      "variables": { "api_key": "internal-key" }
    }
  ]
}

This snippet maps $request.jwt.sub into the x-user-id upstream header. You can map any claim from the JWT payload, including custom claims like org_id or role, using the same $request.jwt.<claim> syntax.

Troubleshooting

• If a mapped header arrives empty at the upstream, verify the source exists: check that the JWT claim is present in the token, the request header was sent by the client, or the variable is defined in config.

• If $request.jwt.sub is null on a route without auth: true, remember that JWT claims are only available after successful token validation -- add auth: true to the route.

• If route variables are not overriding global variables, confirm the variable name matches exactly (case-sensitive) and that the route-level variables block is inside the path entry, not at the top level.

• Use a tool like jwt.io to decode your test token and confirm the claim names match what your mapping expects (e.g., sub vs user_id).

Related docs

• README

• priority variables

• gateway troubleshooting matrix