API Authentication

The Nuts node’s /internal HTTP endpoints can be configured to require signed JWT tokens before allowing calls.

When enabled you need to pass a bearer token as Authorization header:

Authorization: Bearer (token)

When authentication fails the API will return HTTP 401 Unauthorized. The logs on the nuts-node will provide an explanation about the failure.

Note

The JWTs and private keys used in this authentication scheme are secrets and should never be shared with anyone. No one should ever ask you to send them your JWTs or private keys.

Configuration

Authentication can be enabled by setting http.internal.auth.type (see example below) to token_v2. Endpoints under /internal will then require a JWT signed by an authorized key.

Authorized (public) keys are specified in an authorized_keys file configured by the http.internal.auth.type.authorizedkeyspath parameter. This file should contain one or more trusted keys, in the standard SSH format. ECDSA, Ed25519, and RSA (>=2048-bit) keys are accepted. Each line in the file must contain the key-type, key-specification, and user name that is authorized, for example ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIH1VNKtThJiI6c5zjLn/6EjRq1PtfM4qw4HM71zivIVn john.doe@company.com. Note that this file should be a distinct authorized_keys file from that used to grant console access to the nuts node. API access and SSH access are two entirely different matters and we are simply using this well known configuration file format. The Nuts node does not integrate in any way with the SSH subsystem on the host OS.

http:
  internal:
    auth:
      type: token_v2                                 # enables authentication
      authorizedkeyspath: /opt/nuts/authorized_keys  # path to the file containing public keys that are allowed to authenticate.
                                                     # JWTs must be signed with a key registered in this file,
      audience: nuts-node.example.com                # audience for the JWT, defaults to the machine's host name

JWT requirements

JWT’s can be generated in code and must meet the following requirements:

  • The iss field must be present

  • The iss field must match the username specified in the comment of an authorized_keys entry

  • The sub field must be present and non-empty (set it to the issuer if you are unsure which value to use)

  • The iat field must be present

  • The nbf field must be present

  • The iat value must occur at or before the nbf value

  • The exp field must be present

  • The exp value must occur no more than 24 hours after the iat value

  • The jti field must be present and contain a UUID string

  • The aud field must be present

  • The aud field must contain the configured auth.audience parameter (hostname by default) on the nuts node

  • The JWT must be signed by a known ECDSA, Ed25519, or RSA (>=2048-bit) key as configured in auth.authorizedkeyspath

  • Signatures based on RSA keys may use the RS512 or PS512 algorithms only

  • The kid field must contain either the JWK SHA-256 Thumbprint (e.g. NzbLsXh8uDCcd-6MNwXF4W_7noWXFZAfHkxZsRGC9Xs) or the SSH SHA-256 fingerprint (e.g. SHA256:G5hwd24Zl7dyTsAGVxqyZk6z+oJ5UxWcIRL3fWGj7wk) of the signing key

  • The JWT must not be encrypted

The following entries MUST NOT be present:

  • The jwk field (embeds the public key)

  • The jku field (embeds a URL for fetching the public key)

  • The x5c field (embeds an X.509 certificate chain,)

  • The x5u field (embeds a URL for fetching the public key in X.509 form)

Implementing API Authentication

Generally speaking for your application to access the protected API endpoints the following process must be followed:

  1. Generate a private Ed25519, ECDSA, or RSA (>=2048-bit) key. Use Ed25519 if unsure which type to use.

  2. Generate an authorized_keys entry for your public key and configure the Nuts node with it (see below).

  3. Create a JWT, meeting the above specifications

  4. Sign the JWT using the key generated in step 1.

  5. Include the encoded JWT as a bearer token in the Authorization header of API requests.

  6. Stop using the JWT before it expires, rotating it for a freshly generated JWT.

  7. Be careful to keep your JWTs out of log messages etc., and treat them as secret at all times.

The following events are audited concerning API authentication: - AccessKeyRegistered for each authorized key, on startup. - AccessDenied when a JWT fails to authenticate. - AccessGranted when a JWT successfully authenticates.

Generating authorized_keys file

authorized_keys files are made up of multiple lines, each line specifying one more key/user that is authorized. For more information on the authorized_keys format see the AUTHORIZED_KEYS FILE FORMAT section of the man page.

The following is an example authorized_keys file. Each line specifies the key type, the public key, and the username:

ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBAPwLGkaO5dWEx29sW4xnmv/s8+Nzj3mnkY6SX9Qnb91oyPayZV8Ts3TXSMKlkyYHVcIz/nAxRgxgKBTMwZc2wE= alice@company.com
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAwaOa7iN1gnKEfiZAA7lhu3SIvfdzYE3VbswsVUQP7F bob@company.com
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIH1VNKtThJiI6c5zjLn/6EjRq1PtfM4qw4HM71zivIVn dan@company.com
ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBC54Az33UVYdRSTb/2N9LiZtL7TRiEox5+rJcnMYz+t30l4UG5Y8ZN6L2dJCCFWyQeeJ/oTOY915L9/miklDyhk= heidi@company.com
To generate a key’s authorized_keys form using ssh-keygen:
ssh-keygen -y -f /path/to/keyfile

Generating kid field

You can use ssh-keygen to generate the SSH fingerprint (used in the kid field) of a key:

ssh-keygen -lf /path/to/keyfile

nuts-jwt-generator

The nuts-jwt-generator is a command-line tool that can be used to generate JWTs and authorized_keys entries. For instance, when ssh-keygen is unavailable on your platform or when using Ed25519 keys (see below). It is available on the nuts-foundation GitHub page.

To generate a key’s authorized_keys form (for configuration of the Nuts node) using nuts-jwt-generator:

nuts-jwt-generator -i /path/to/keyfile --export-authorized-key

To generate the SSH fingerprint of a key (for specifying as kid field) using nuts-jwt-generator:

nuts-jwt-generator -i /path/to/keyfile -export-ssh-fingerprint

The ssh-keygen` command unfortunately fails for Ed25519 PEM keys at the time of this writing due to a bug and poor recent support for Ed25519 in libcrypto packages. You can use the nuts-jwt-generator until this bug is fixed for keys of this type.

Generating keys

Just for reference, this section lists various commands to generate key pairs for signing JWTs, using ssh-keygen and openssl.

To generate an ECDSA key using ssh-keygen:

ssh-keygen -t ecdsa -b 521 -f /path/to/keyfile

To generate an RSA key using ssh-keygen:

ssh-keygen -t rsa -b 4096 -f /path/to/keyfile

To generate an Ed25519 key with using ssh-keygen:

ssh-keygen -t ed25519 -f /path/to/keyfile

To generate an ECDSA key with OpenSSL:

openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:P-521 -pkeyopt ec_param_enc:named_curve -out /path/to/keyfile.pem

To generate an RSA key with OpenSSL:

openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:4096 -out /path/to/rsa-private.pem

To generate an Ed25519 key with OpenSSL:

openssl genpkey -algorithm ed25519 -out /path/to/keyfile.pem