Parameters & Claims Reference

Registered Claims (RFC 7519 §4.1)

These are the standard payload fields reserved by RFC 7519. They are all optional, but higher-level specifications such as OAuth2 / OIDC make them required as needed.

Claim	Full Name	Meaning
`iss`	Issuer	Issuer identifier, usually the HTTPS URL of the AS/OP
`sub`	Subject	The subject (the entity the token describes), unique within the scope of `iss`
`aud`	Audience	The intended recipient(s) of the token; may be a string or an array
`exp`	Expiration Time	Expiration time (Unix seconds); must be rejected after this
`nbf`	Not Before	Time it becomes valid (Unix seconds); must be rejected before this
`iat`	Issued At	Issue time (Unix seconds)
`jti`	JWT ID	Unique token identifier, usable for replay protection / blacklisting

Time claims are all in Unix seconds

exp / nbf / iat are all seconds since 1970-01-01 UTC (not milliseconds). When validating, allow a small clock skew, typically ≤ 300 seconds.

Common Header Fields

Field	Meaning
`alg`	Signature/encryption algorithm (see table below)
`typ`	Token type: `JWT`; RFC 9068 access tokens use `at+jwt`; logout tokens use `logout+jwt`
`kid`	Key ID, used with JWKS to locate the verification public key
`cty`	Content type, used for nested JWTs
`jku` / `x5c` / `x5t`	A URL pointing to a key / a certificate chain / a certificate thumbprint (accepting an external `jku` is risky and requires caution)

`alg`	Description	Key Type
`HS256` / `HS384` / `HS512`	HMAC + SHA-2	Symmetric shared secret
`RS256` / `RS384` / `RS512`	RSASSA-PKCS1-v1_5 + SHA-2	RSA public/private key
`PS256` / `PS384` / `PS512`	RSASSA-PSS + SHA-2	RSA public/private key
`ES256` / `ES384` / `ES512`	ECDSA + SHA-2	EC public/private key
`EdDSA`	Ed25519 / Ed448 (RFC 8037)	OKP public/private key
`none`	No signature	—

In production you must maintain an alg allowlist and reject none, and also pin the expected algorithm family to prevent RS256→HS256 confusion attacks. See Core Concepts · Three Fatal Verification Pitfalls.

Common JWE Encryption Algorithms (RFC 7518, when confidentiality is needed)

Purpose	Example Values
Key management (`alg`)	`RSA-OAEP`, `ECDH-ES`, `A256KW`
Content encryption (`enc`)	`A128GCM`, `A256GCM`, `A256CBC-HS512`

Base64URL

Each segment of a JWT is encoded with Base64URL (RFC 4648 §5), which differs from standard Base64 as follows:

+ → -, / → _
Trailing = padding is removed

The goal is to let the token be safely placed in URLs and HTTP headers. Convert between them with the Base64URL Encoder/Decoder.

RFC	Title
RFC 7515	JSON Web Signature (JWS)
RFC 7516	JSON Web Encryption (JWE)
RFC 7517	JSON Web Key (JWK)
RFC 7518	JSON Web Algorithms (JWA)
RFC 7519	JSON Web Token (JWT)
RFC 7662	OAuth 2.0 Token Introspection
RFC 8037	CFRG-curve usage in JOSE (EdDSA, etc.)
RFC 9068	JWT Profile for OAuth 2.0 Access Tokens

JWT Decoder — decoding and verification
JWT Signer — build test tokens
JWK Generator · JWK → PEM · PEM → JWK
Base64URL Encoder/Decoder