Add a method to decode a token without signature validation

- Solves Keats#48
- `dangerous_unsafe_decode`
- No docs (aside from cargo) since people probably shouldn't use it

src/lib.rs

@@ -122,6 +122,39 @@ pub fn decode<T: DeserializeOwned>(token: &str, key: &[u8], validation: &Validat
     Ok(TokenData { header: header, claims: decoded_claims })
 }
 
+/// Decode a token without any signature validation into a struct containing 2 fields: `claims` and `header`.
+///
+/// NOTE: Do not use this unless you know what you are doing! If the token's signature is invalid, it will *not* return an error.
+///
+/// ```rust,ignore
+/// #[macro_use]
+/// extern crate serde_derive;
+/// use jsonwebtoken::{dangerous_unsave_decode, Validation, Algorithm};
+///
+/// #[derive(Debug, Serialize, Deserialize)]
+/// struct Claims {
+///     sub: String,
+///     company: String
+/// }
+///
+/// let token = "a.jwt.token".to_string();
+/// // Claims is a struct that implements Deserialize
+/// let token_data = dangerous_unsafe_decode::<Claims>(&token, &Validation::new(Algorithm::HS256));
+/// ```
+pub fn dangerous_unsafe_decode<T: DeserializeOwned>(token: &str, validation: &Validation) -> Result<TokenData<T>> {
+    let (_, signing_input) = expect_two!(token.rsplitn(2, '.'));
+    let (claims, header) = expect_two!(signing_input.rsplitn(2, '.'));
+    let header: Header = from_jwt_part(header)?;
+
+    if !validation.algorithms.contains(&header.alg) {
+        return Err(ErrorKind::InvalidAlgorithm.into());
+    }
+
+    let (decoded_claims, _): (T, _)  = from_jwt_part_claims(claims)?;
+
+    Ok(TokenData { header: header, claims: decoded_claims })
+}
+
 /// Decode a token and return the Header. This is not doing any kind of validation: it is meant to be
 /// used when you don't know which `alg` the token is using and want to find out.
 ///

tests/lib.rs

@@ -2,7 +2,7 @@ extern crate jsonwebtoken;
 #[macro_use]
 extern crate serde_derive;
 
-use jsonwebtoken::{encode, decode, decode_header, Algorithm, Header, sign, verify, Validation};
+use jsonwebtoken::{encode, decode, decode_header, dangerous_unsafe_decode, Algorithm, Header, sign, verify, Validation};
 
 
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
@@ -103,3 +103,33 @@ fn decode_header_only() {
     assert_eq!(header.alg, Algorithm::HS256);
     assert_eq!(header.typ, Some("JWT".to_string()));
 }
+
+#[test]
+fn dangerous_unsafe_decode_token() {
+    let token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJiQGIuY29tIiwiY29tcGFueSI6IkFDTUUifQ.I1BvFoHe94AFf09O6tDbcSB8-jp8w6xZqmyHIwPeSdY";
+    let claims = dangerous_unsafe_decode::<Claims>(token, &Validation::default());
+    claims.unwrap();
+}
+
+#[test]
+#[should_panic(expected = "InvalidToken")]
+fn dangerous_unsafe_decode_token_missing_parts() {
+    let token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9";
+    let claims = dangerous_unsafe_decode::<Claims>(token, &Validation::default());
+    claims.unwrap();
+}
+
+#[test]
+fn dangerous_unsafe_decode_token_invalid_signature() {
+    let token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJiQGIuY29tIiwiY29tcGFueSI6IkFDTUUifQ.wrong";
+    let claims = dangerous_unsafe_decode::<Claims>(token, &Validation::default());
+    claims.unwrap();
+}
+
+#[test]
+#[should_panic(expected = "InvalidAlgorithm")]
+fn dangerous_unsafe_decode_token_wrong_algorithm() {
+    let token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJiQGIuY29tIiwiY29tcGFueSI6IkFDTUUifQ.I1BvFoHe94AFf09O6tDbcSB8-jp8w6xZqmyHIwPeSdY";
+    let claims = dangerous_unsafe_decode::<Claims>(token, &Validation::new(Algorithm::RS512));
+    claims.unwrap();
+}