To sign a JWT with ES256 in Rust, the jsonwebtoken crate's encode takes a Header, a Serialize claims struct and an EncodingKey loaded from a PKCS#8 PEM. Since version 10 the crate needs an explicit crypto backend feature; the run builds with rust_crypto and checks the token with OpenSSL.

Cargo.toml — jsonwebtoken with the pure-Rust backend

1[dependencies]
2# jsonwebtoken 10+ needs a crypto backend: "rust_crypto" (pure Rust) or "aws_lc_rs"
3jsonwebtoken = { version = "=11.1.0", features = ["rust_crypto"] }
4serde = { version = "=1.0.229", features = ["derive"] }

src/main.rs — ES256 with jsonwebtoken

1use std::time::{SystemTime, UNIX_EPOCH};
2 
3use jsonwebtoken::{encode, Algorithm, EncodingKey, Header};
4use serde::Serialize;
5 
6#[derive(Serialize)]
7struct Claims<'a> {
8    iss: &'a str,
9    sub: &'a str,
10    aud: &'a str,
11    iat: u64,
12    exp: u64,
13}
14 
15fn main() -> Result<(), Box<dyn std::error::Error>> {
16    // from_ec_pem wants PKCS#8 ("BEGIN PRIVATE KEY")
17    let key = EncodingKey::from_ec_pem(&std::fs::read("key.pem")?)?;
18 
19    let mut header = Header::new(Algorithm::ES256);
20    header.kid = Some("2026-10".to_owned());
21 
22    let now = SystemTime::now().duration_since(UNIX_EPOCH)?.as_secs();
23    let claims = Claims {
24        iss: "https://issuer.example.com",
25        sub: "user-42",
26        aud: "api://orders",
27        iat: now,
28        exp: now + 15 * 60,
29    };
30 
31    println!("{}", encode(&header, &claims, &key)?);
32    Ok(())
33}

How it works

EncodingKey::from_ec_pem reads a BEGIN PRIVATE KEY (PKCS#8) block.
Header::new(Algorithm::ES256) sets alg and typ; header.kid adds the key id.
The claims are any Serialize type; iat and exp are u64 seconds from SystemTime.
encode returns the compact token as a String.

Gotchas

Without the rust_crypto or aws_lc_rs feature, the code still compiles and then panics at the first signature: Could not automatically determine the process-level CryptoProvider from jsonwebtoken crate features.
from_ec_pem rejects SEC 1 keys (BEGIN EC PRIVATE KEY) with Error(InvalidKeyFormat). Convert them with openssl pkcs8 -topk8 -nocrypt -in ec.pem -out key.pem.
Choose exactly one backend: with both features enabled, jsonwebtoken cannot pick a provider automatically and you must install one with CryptoProvider::install_default().
Use a struct for claims rather than serde_json::Value with ad-hoc fields: the types catch a string exp or a missing aud at compile time.

How to sign a JWT with ES256 in Rust

How it works

Gotchas

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