# Getting the user's identity
This article describes how to retrieve a user's identity from a pomerium managed application. Pomerium uses JSON Web Tokens (JWT) to attest that a given request was handled by Pomerium's authorizer service.
# Prerequisites
To secure your app with signed headers, you'll need the following:
- An application you want users to connect to.
- A JWT library that supports the
ES256
algorithm.
# Verification
A JWT attesting to the authorization of a given request is added to the downstream HTTP request header x-pomerium-jwt-assertion
. You should verify that the JWT contains at least the following claims:
JWT | description |
---|---|
exp | Expiration time in seconds since the UNIX epoch. Allow 1 minute for skew. |
iat | Issued-at time in seconds since the UNIX epoch. Allow 1 minute for skew. |
aud | The client's final domain e.g. httpbin.corp.example.com . |
iss | Issuer must be the URL of your authentication domain e.g. authenticate.corp.example . |
sub | Subject is the user's id. Can be used instead of the x-pomerium-authenticated-user-id header. |
email | Email is the user's email. Can be used instead of the x-pomerium-authenticated-user-email header. |
groups | Groups is the user's groups. Can be used instead of the x-pomerium-authenticated-user-groups header. |
# Manual verification
Though you will very likely be verifying signed-headers programmatically in your application's middleware, and using a third-party JWT library, if you are new to JWT it may be helpful to show what manual verification looks like. The following guide assumes you are using the provided docker-compose.yml as a base and httpbin. Httpbin gives us a convenient way of inspecting client headers.
- Provide pomerium with a base64 encoded Elliptic Curve (NIST P-256 aka secp256r1 aka prime256v1) Private Key. In production, you'd likely want to get these from your KMS.
# see ./scripts/generate_self_signed_signing_key.sh
openssl ecparam -genkey -name prime256v1 -noout -out ec_private.pem
openssl req -x509 -new -key ec_private.pem -days 1000000 -out ec_public.pem -subj "/CN=unused"
# careful! this will output your private key in terminal
cat ec_private.pem | base64
Copy the base64 encoded value of your private key to pomerium-proxy
's environmental configuration variable SIGNING_KEY
.
SIGNING_KEY=ZxqyyIPPX0oWrrOwsxXgl0hHnTx3mBVhQ2kvW1YB4MM=
- Reload
pomerium-proxy
. Navigate to httpbin (by default,https://httpbin.corp.${YOUR-DOMAIN}.com
), and login as usual. Click request inspection. Select `/headers'. Click try it out and then execute. You should see something like the following.
X-Pomerium-Jwt-Assertion
is the signature value. It's less scary than it looks and basically just a compressed, json blob as described above. Navigate to jwt.io which provides a helpful GUI to manually verify JWT values.Paste the value of
X-Pomerium-Jwt-Assertion
header token into theEncoded
form. You should notice that the decoded values look much more familiar.
- Finally, we want to cryptographically verify the validity of the token. To do this, we will need the signer's public key. You can simply copy and past the output of
cat ec_public.pem
.
Viola! Hopefully walking through a manual verification has helped give you a better feel for how signed JWT tokens are used as a secondary validation mechanism in pomerium.
WARNING
In an actual client, you'll want to ensure that all the other claims values are valid (like expiration, issuer, audience and so on) in the context of your application. You'll also want to make sure you have a safe and reliable mechanism for distributing pomerium-proxy's public signing key to client apps (typically, a key management service).
# Automatic verification
In the future, we will be adding example client implementations for:
- Python
- Go
- Java
- C#
- PHP