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

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 +65,11 @@ pub struct Header {
     #[serde(skip_serializing_if = "Option::is_none")]
     #[serde(rename = "x5t#S256")]
     pub x5t_s256: Option<String>,
+
+    /// Any additional headers
+    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(flatten)]
+    pub extra: Option<HashMap<String, String>>,
 }
 
 impl Header {
@@ -80,6 +86,7 @@ impl Header {
             x5c: None,
             x5t: None,
             x5t_s256: None,
+            extra: None
         }
     }
 

tests/hmac.rs

@@ -1,3 +1,4 @@
+use std::collections::HashMap;
 use jsonwebtoken::errors::ErrorKind;
 use jsonwebtoken::jwk::Jwk;
 use jsonwebtoken::{
@@ -41,7 +42,9 @@ fn encode_with_custom_header() {
         company: "ACME".to_string(),
         exp: OffsetDateTime::now_utc().unix_timestamp() + 10000,
     };
-    let header = Header { kid: Some("kid".to_string()), ..Default::default() };
+    let mut extra = HashMap::with_capacity(1);
+    extra.insert("custom".to_string(), "header".to_string());
+    let header = Header { kid: Some("kid".to_string()), extra: Some(extra), ..Default::default() };
     let token = encode(&header, &my_claims, &EncodingKey::from_secret(b"secret")).unwrap();
     let token_data = decode::<Claims>(
         &token,
@@ -51,6 +54,7 @@ fn encode_with_custom_header() {
     .unwrap();
     assert_eq!(my_claims, token_data.claims);
     assert_eq!("kid", token_data.header.kid.unwrap());
+    assert_eq!("header", token_data.header.extra.unwrap().get("custom").unwrap().as_str());
 }
 
 #[test]