feat: allow users to specify a custom header not defined in the struct

README.md

@@ -79,6 +79,11 @@ If you want to set the `kid` parameter or change the algorithm for example:
 ```rust
 let mut header = Header::new(Algorithm::HS512);
 header.kid = Some("blabla".to_owned());
+
+let mut extras = HashMap::with_capacity(1);
+extras.insert("custom".to_string(), "header".to_string());
+header.extras = Some(extras);
+
 let token = encode(&header, &my_claims, &EncodingKey::from_secret("secret".as_ref()))?;
 ```
 Look at `examples/custom_header.rs` for a full working example.

benches/jwt.rs

@@ -1,6 +1,7 @@
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 use jsonwebtoken::{decode, encode, Algorithm, DecodingKey, EncodingKey, Header, Validation};
 use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
 
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
 struct Claims {
@@ -17,6 +18,18 @@ fn bench_encode(c: &mut Criterion) {
     });
 }
 
+fn bench_encode_custom_extra_headers(c: &mut Criterion) {
+    let claim = Claims { sub: "[email protected]".to_owned(), company: "ACME".to_owned() };
+    let key = EncodingKey::from_secret("secret".as_ref());
+    let mut extras = HashMap::with_capacity(1);
+    extras.insert("custom".to_string(), "header".to_string());
+    let header = &Header { extras, ..Default::default() };
+
+    c.bench_function("bench_encode", |b| {
+        b.iter(|| encode(black_box(header), black_box(&claim), black_box(&key)))
+    });
+}
+
 fn bench_decode(c: &mut Criterion) {
     let token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ";
     let key = DecodingKey::from_secret("secret".as_ref());
@@ -32,5 +45,5 @@ fn bench_decode(c: &mut Criterion) {
     });
 }
 
-criterion_group!(benches, bench_encode, bench_decode);
+criterion_group!(benches, bench_encode, bench_encode_custom_extra_headers, bench_decode);
 criterion_main!(benches);

examples/custom_header.rs

@@ -1,4 +1,5 @@
 use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
 
 use jsonwebtoken::errors::ErrorKind;
 use jsonwebtoken::{decode, encode, Algorithm, DecodingKey, EncodingKey, Header, Validation};
@@ -15,8 +16,15 @@ fn main() {
         Claims { sub: "[email protected]".to_owned(), company: "ACME".to_owned(), exp: 10000000000 };
     let key = b"secret";
 
-    let header =
-        Header { kid: Some("signing_key".to_owned()), alg: Algorithm::HS512, ..Default::default() };
+    let mut extras = HashMap::with_capacity(1);
+    extras.insert("custom".to_string(), "header".to_string());
+
+    let header = Header {
+        kid: Some("signing_key".to_owned()),
+        alg: Algorithm::HS512,
+        extras,
+        ..Default::default()
+    };
 
     let token = match encode(&header, &my_claims, &EncodingKey::from_secret(key)) {
         Ok(t) => t,

src/header.rs

@@ -1,3 +1,4 @@
+use std::collections::HashMap;
 use std::result;
 
 use base64::{engine::general_purpose::STANDARD, Engine};
@@ -10,7 +11,7 @@ use crate::serialization::b64_decode;
 
 /// A basic JWT header, the alg defaults to HS256 and typ is automatically
 /// set to `JWT`. All the other fields are optional.
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, Hash)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct Header {
     /// The type of JWS: it can only be "JWT" here
     ///
@@ -64,6 +65,12 @@ pub struct Header {
     #[serde(skip_serializing_if = "Option::is_none")]
     #[serde(rename = "x5t#S256")]
     pub x5t_s256: Option<String>,
+
+    /// Any additional non-standard headers not defined in [RFC7515#4.1](https://datatracker.ietf.org/doc/html/rfc7515#section-4.1).
+    /// Once serialized, all keys will be converted to fields at the root level of the header payload
+    /// Ex: Dict("custom" -> "header") will be converted to "{"typ": "JWT", ..., "custom": "header"}"
+    #[serde(flatten)]
+    pub extras: HashMap<String, String>,
 }
 
 impl Header {
@@ -80,6 +87,7 @@ impl Header {
             x5c: None,
             x5t: None,
             x5t_s256: None,
+            extras: Default::default(),
         }
     }
 

src/jwk.rs

@@ -43,7 +43,7 @@ impl<'de> Deserialize<'de> for PublicKeyUse {
         D: Deserializer<'de>,
     {
         struct PublicKeyUseVisitor;
-        impl<'de> de::Visitor<'de> for PublicKeyUseVisitor {
+        impl de::Visitor<'_> for PublicKeyUseVisitor {
             type Value = PublicKeyUse;
 
             fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -116,7 +116,7 @@ impl<'de> Deserialize<'de> for KeyOperations {
         D: Deserializer<'de>,
     {
         struct KeyOperationsVisitor;
-        impl<'de> de::Visitor<'de> for KeyOperationsVisitor {
+        impl de::Visitor<'_> for KeyOperationsVisitor {
             type Value = KeyOperations;
 
             fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {

src/serialization.rs

@@ -3,10 +3,12 @@ use serde::{Deserialize, Serialize};
 
 use crate::errors::Result;
 
+#[inline]
 pub(crate) fn b64_encode<T: AsRef<[u8]>>(input: T) -> String {
     URL_SAFE_NO_PAD.encode(input)
 }
 
+#[inline]
 pub(crate) fn b64_decode<T: AsRef<[u8]>>(input: T) -> Result<Vec<u8>> {
     URL_SAFE_NO_PAD.decode(input).map_err(|e| e.into())
 }

src/validation.rs

@@ -337,13 +337,20 @@ where
 {
     struct NumericType(PhantomData<fn() -> TryParse<u64>>);
 
-    impl<'de> Visitor<'de> for NumericType {
+    impl Visitor<'_> for NumericType {
         type Value = TryParse<u64>;
 
         fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
             formatter.write_str("A NumericType that can be reasonably coerced into a u64")
         }
 
+        fn visit_u64<E>(self, value: u64) -> std::result::Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            Ok(TryParse::Parsed(value))
+        }
+
         fn visit_f64<E>(self, value: f64) -> std::result::Result<Self::Value, E>
         where
             E: de::Error,
@@ -354,13 +361,6 @@ where
                 Err(serde::de::Error::custom("NumericType must be representable as a u64"))
             }
         }
-
-        fn visit_u64<E>(self, value: u64) -> std::result::Result<Self::Value, E>
-        where
-            E: de::Error,
-        {
-            Ok(TryParse::Parsed(value))
-        }
     }
 
     match deserializer.deserialize_any(NumericType(PhantomData)) {

tests/hmac.rs

@@ -5,6 +5,7 @@ use jsonwebtoken::{
     decode, decode_header, encode, Algorithm, DecodingKey, EncodingKey, Header, Validation,
 };
 use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
 use time::OffsetDateTime;
 use wasm_bindgen_test::wasm_bindgen_test;
 
@@ -51,6 +52,56 @@ fn encode_with_custom_header() {
     .unwrap();
     assert_eq!(my_claims, token_data.claims);
     assert_eq!("kid", token_data.header.kid.unwrap());
+    assert!(token_data.header.extras.is_empty());
+}
+
+#[test]
+#[wasm_bindgen_test]
+fn encode_with_extra_custom_header() {
+    let my_claims = Claims {
+        sub: "[email protected]".to_string(),
+        company: "ACME".to_string(),
+        exp: OffsetDateTime::now_utc().unix_timestamp() + 10000,
+    };
+    let mut extras = HashMap::with_capacity(1);
+    extras.insert("custom".to_string(), "header".to_string());
+    let header = Header { kid: Some("kid".to_string()), extras, ..Default::default() };
+    let token = encode(&header, &my_claims, &EncodingKey::from_secret(b"secret")).unwrap();
+    let token_data = decode::<Claims>(
+        &token,
+        &DecodingKey::from_secret(b"secret"),
+        &Validation::new(Algorithm::HS256),
+    )
+    .unwrap();
+    assert_eq!(my_claims, token_data.claims);
+    assert_eq!("kid", token_data.header.kid.unwrap());
+    assert_eq!("header", token_data.header.extras.get("custom").unwrap().as_str());
+}
+
+#[test]
+#[wasm_bindgen_test]
+fn encode_with_multiple_extra_custom_headers() {
+    let my_claims = Claims {
+        sub: "[email protected]".to_string(),
+        company: "ACME".to_string(),
+        exp: OffsetDateTime::now_utc().unix_timestamp() + 10000,
+    };
+    let mut extras = HashMap::with_capacity(2);
+    extras.insert("custom1".to_string(), "header1".to_string());
+    extras.insert("custom2".to_string(), "header2".to_string());
+    let header = Header { kid: Some("kid".to_string()), extras, ..Default::default() };
+    let token = encode(&header, &my_claims, &EncodingKey::from_secret(b"secret")).unwrap();
+    let token_data = decode::<Claims>(
+        &token,
+        &DecodingKey::from_secret(b"secret"),
+        &Validation::new(Algorithm::HS256),
+    )
+    .unwrap();
+    assert_eq!(my_claims, token_data.claims);
+    assert_eq!("kid", token_data.header.kid.unwrap());
+    let extras = token_data.header.extras;
+    assert_eq!("header1", extras.get("custom1").unwrap().as_str());
+    assert_eq!("header2", extras.get("custom2").unwrap().as_str());
 }
 
 #[test]
@@ -86,6 +137,25 @@ fn decode_token() {
     claims.unwrap();
 }
 
+#[test]
+#[wasm_bindgen_test]
+fn decode_token_custom_headers() {
+    let token = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiIsImtpZCI6ImtpZCIsImN1c3RvbTEiOiJoZWFkZXIxIiwiY3VzdG9tMiI6ImhlYWRlcjIifQ.eyJzdWIiOiJiQGIuY29tIiwiY29tcGFueSI6IkFDTUUiLCJleHAiOjI1MzI1MjQ4OTF9.FtOHsoKcNH3SriK3tnR-uWJg4UV4FkOzvq_JCfLngfU";
+    let claims = decode::<Claims>(
+        token,
+        &DecodingKey::from_secret(b"secret"),
+        &Validation::new(Algorithm::HS256),
+    )
+    .unwrap();
+    let my_claims =
+        Claims { sub: "[email protected]".to_string(), company: "ACME".to_string(), exp: 2532524891 };
+    assert_eq!(my_claims, claims.claims);
+    assert_eq!("kid", claims.header.kid.unwrap());
+    let extras = claims.header.extras;
+    assert_eq!("header1", extras.get("custom1").unwrap().as_str());
+    assert_eq!("header2", extras.get("custom2").unwrap().as_str());
+}
+
 #[test]
 #[wasm_bindgen_test]
 #[should_panic(expected = "InvalidToken")]