Ensure array_type has front() method + fix array_type on jsoncpp (#361)

* Use operator[] instead of front to support jsoncpp

Replace the `front()` with `[0]` as front is not supported by jsoncpp on
array types.

Signed-off-by: Omar Mohamed <mohamed.omar67492@gmail.com>

* Revert "Use operator[] instead of front to support jsoncpp"

This reverts commit dfa7d29.

* Implement `front()` in jsoncpp array_type

Signed-off-by: Omar Mohamed <mohamed.omar67492@gmail.com>

* Check if array_type has a front() method

Signed-off-by: Omar Mohamed <mohamed.omar67492@gmail.com>

* Add `front()` to jsoncons array_type

* Remove non-const overloads of front()

Signed-off-by: Omar Mohamed <mohamed.omar67492@gmail.com>

* Fix check for front() in array_type

Signed-off-by: Omar Mohamed <mohamed.omar67492@gmail.com>

* Use std::decay

Signed-off-by: Omar Mohamed <mohamed.omar67492@gmail.com>

* fix example to print array value

* expose base class ctors

* update as_array traits helper

* fixup linter

---------

Signed-off-by: Omar Mohamed <mohamed.omar67492@gmail.com>
Co-authored-by: Chris Mc <prince.chrismc@gmail.com>

Author: omar-mohamed-khallaf

example/traits/danielaparker-jsoncons.cpp

@@ -34,7 +34,7 @@ int main() {
 	const auto decoded = jwt::decode<traits>(token);
 
 	const auto array = traits::as_array(decoded.get_payload_claim("object").to_json()["api"]["array"]);
-	std::cout << "payload /object/api/array = " << array << std::endl;
+	std::cout << "payload /object/api/array = " << jsoncons::pretty_print(traits::json(array)) << std::endl;
 
 	jwt::verify<traits>()
 		.allow_algorithm(jwt::algorithm::none{})

include/jwt-cpp/jwt.h

@@ -808,7 +808,7 @@ namespace jwt {
 		 * \brief Load a public key from a string.
 		 *
 		 * The string should contain a pem encoded certificate or public key
-		 * 
+		 *
 		 * \deprecated Use the templated version helper::load_private_key_from_string with error::ecdsa_error
 		 *
 		 * \param key		String containing the certificate encoded as pem
@@ -872,7 +872,7 @@ namespace jwt {
 		 * The string should contain a pem encoded certificate or public key
 		 *
 		 * \deprecated Use the templated version helper::load_private_key_from_string with error::ecdsa_error
-		 * 
+		 *
 		 * \param key		String containing the certificate or key encoded as pem
 		 * \param password	Password used to decrypt certificate or key (leave empty if not encrypted)
 		 * \throw			ecdsa_exception if an error occurred
@@ -887,7 +887,7 @@ namespace jwt {
 
 		/**
 		 * \brief Load a private key from a string.
-		 * 
+		 *
 		 * \deprecated Use the templated version helper::load_private_key_from_string with error::ecdsa_error
 		 *
 		 * \param key		String containing a private key as pem
@@ -1077,7 +1077,7 @@ namespace jwt {
 		 * \brief Load a private key from a string.
 		 *
 		 * \deprecated Use the templated version helper::load_private_key_from_string with error::ecdsa_error
-		 * 
+		 *
 		 * \param key		String containing a private key as pem
 		 * \param password	Password used to decrypt key (leave empty if not encrypted)
 		 * \throw			ecdsa_exception if an error occurred
@@ -1372,7 +1372,7 @@ namespace jwt {
 		struct hmacsha {
 			/**
 			 * Construct new hmac algorithm
-			 * 
+			 *
 			 * \param key Key to use for HMAC
 			 * \param md Pointer to hash function
 			 * \param name Name of the algorithm
@@ -1381,7 +1381,7 @@ namespace jwt {
 				: secret(std::move(key)), md(md), alg_name(std::move(name)) {}
 			/**
 			 * Sign jwt data
-			 * 
+			 *
 			 * \param data The data to sign
 			 * \param ec error_code filled with details on error
 			 * \return HMAC signature for the given data
@@ -1402,7 +1402,7 @@ namespace jwt {
 			}
 			/**
 			 * Check if signature is valid
-			 * 
+			 *
 			 * \param data The data to check signature against
 			 * \param signature Signature provided by the jwt
 			 * \param ec Filled with details about failure.
@@ -1423,7 +1423,7 @@ namespace jwt {
 			}
 			/**
 			 * Returns the algorithm name provided to the constructor
-			 * 
+			 *
 			 * \return algorithm's name
 			 */
 			std::string name() const { return alg_name; }
@@ -1442,7 +1442,7 @@ namespace jwt {
 		struct rsa {
 			/**
 			 * Construct new rsa algorithm
-			 * 
+			 *
 			 * \param public_key RSA public key in PEM format
 			 * \param private_key RSA private key or empty string if not available. If empty, signing will always fail.
 			 * \param public_key_password Password to decrypt public key pem.
@@ -1495,7 +1495,7 @@ namespace jwt {
 			}
 			/**
 			 * Check if signature is valid
-			 * 
+			 *
 			 * \param data The data to check signature against
 			 * \param signature Signature provided by the jwt
 			 * \param ec Filled with details on failure
@@ -2053,13 +2053,13 @@ namespace jwt {
 		};
 		/**
 		 * RS256 algorithm.
-		 * 
+		 *
 		 * This data structure is used to describe the RSA256 and can be used to verify JWTs
 		 */
 		struct rs256 : public rsa {
 			/**
 			 * \brief Construct new instance of algorithm
-			 * 
+			 *
 			 * \param public_key RSA public key in PEM format
 			 * \param private_key RSA private key or empty string if not available. If empty, signing will always fail.
 			 * \param public_key_password Password to decrypt public key pem.
@@ -2459,11 +2459,13 @@ namespace jwt {
 		struct is_valid_json_array {
 			template<typename T>
 			using value_type_t = typename T::value_type;
+			using front_base_type = typename std::decay<decltype(std::declval<array_type>().front())>::type;
 
 			static constexpr auto value = std::is_constructible<value_type, array_type>::value &&
 										  is_iterable<array_type>::value &&
 										  is_detected<value_type_t, array_type>::value &&
-										  std::is_same<typename array_type::value_type, value_type>::value;
+										  std::is_same<typename array_type::value_type, value_type>::value &&
+										  std::is_same<front_base_type, value_type>::value;
 		};
 
 		template<typename string_type, typename integer_type>
@@ -3728,9 +3730,9 @@ namespace jwt {
 		 * Specify a claim to check for using the specified operation.
 		 * This is helpful for implementating application specific authentication checks
 		 * such as the one seen in partial-claim-verifier.cpp
-		 * 
+		 *
 		 * \snippet{trimleft} partial-claim-verifier.cpp verifier check custom claim
-		 * 
+		 *
 		 * \param name Name of the claim to check for
 		 * \param fn Function to use for verifying the claim
 		 * \return *this to allow chaining
@@ -3743,9 +3745,9 @@ namespace jwt {
 		/**
 		 * Specify a claim to check for equality (both type & value).
 		 * See the private-claims.cpp example.
-		 * 
+		 *
 		 * \snippet{trimleft} private-claims.cpp verify exact claim
-		 * 
+		 *
 		 * \param name Name of the claim to check for
 		 * \param c Claim to check for
 		 * \return *this to allow chaining
@@ -3756,13 +3758,13 @@ namespace jwt {
 
 		/**
 		 * \brief Add an algorithm available for checking.
-		 * 
+		 *
 		 * This is used to handle incomming tokens for predefined algorithms
 		 * which the authorization server is provided. For example a small system
 		 * where only a single RSA key-pair is used to sign tokens
-		 * 
+		 *
 		 * \snippet{trimleft} example/rsa-verify.cpp allow rsa algorithm
-		 * 
+		 *
 		 * \tparam Algorithm any algorithm such as those provided by jwt::algorithm
 		 * \param alg Algorithm to allow
 		 * \return *this to allow chaining
@@ -4122,18 +4124,18 @@ namespace jwt {
 	 * Default clock class using std::chrono::system_clock as a backend.
 	 */
 	struct default_clock {
-		/** 
+		/**
 		 * Gets the current system time
-		 * \return time_point of the host system 
+		 * \return time_point of the host system
 		 */
 		date now() const { return date::clock::now(); }
 	};
 
 	/**
 	 * Create a verifier using the default_clock.
-	 * 
-	 * 
-	 * 
+	 *
+	 *
+	 *
 	 * \param c Clock instance to use
 	 * \return verifier instance
 	 */
@@ -4153,7 +4155,7 @@ namespace jwt {
 	/**
 	 * \brief Decode a token. This can be used to to help access important feild like 'x5c'
 	 * for verifying tokens. See associated example rsa-verify.cpp for more details.
-	 * 
+	 *
 	 * \tparam json_traits JSON implementation traits
 	 * \tparam Decode is callable, taking a string_type and returns a string_type.
 	 *         It should ensure the padding of the input and then base64url decode and
@@ -4172,7 +4174,7 @@ namespace jwt {
 	/**
 	 * Decode a token. This can be used to to help access important feild like 'x5c'
 	 * for verifying tokens. See associated example rsa-verify.cpp for more details.
-	 * 
+	 *
 	 * \tparam json_traits JSON implementation traits
 	 * \param token Token to decode
 	 * \return Decoded token
@@ -4194,10 +4196,10 @@ namespace jwt {
 		return jwk<json_traits>(jwk_);
 	}
 	/**
-	 * Parse a JSON Web Key Set. This can be used to to help access 
+	 * Parse a JSON Web Key Set. This can be used to to help access
 	 * important feild like 'x5c' for verifying tokens. See example
 	 * jwks-verify.cpp for more information.
-	 * 
+	 *
 	 * \tparam json_traits JSON implementation traits
 	 * \param jwks_ string buffer containing the JSON object
 	 * \return Parsed JSON object containing the data of the JWK SET string

include/jwt-cpp/traits/danielaparker-jsoncons/traits.h

@@ -61,7 +61,13 @@ namespace jwt {
 					return 0;
 				}
 			};
-			using array_type = json::array;
+			class array_type : public json::array {
+			public:
+				using json::array::array;
+				explicit array_type(const json::array& a) : json::array(a) {}
+				explicit array_type(json::array&& a) : json::array(a) {}
+				value_type const& front() const { return this->operator[](0U); }
+			};
 			using string_type = std::string; // current limitation of traits implementation
 			using number_type = double;
 			using integer_type = int64_t;
@@ -89,7 +95,7 @@ namespace jwt {
 
 			static array_type as_array(const json& val) {
 				if (val.type() != jsoncons::json_type::array_value) throw std::bad_cast();
-				return val.array_value();
+				return array_type(val.array_value());
 			}
 
 			static string_type as_string(const json& val) {

include/jwt-cpp/traits/open-source-parsers-jsoncpp/traits.h

@@ -33,6 +33,8 @@ namespace jwt {
 				~array_type() = default;
 				array_type& operator=(const array_type& o) = default;
 				array_type& operator=(array_type&& o) noexcept = default;
+
+				value_type const& front() const { return this->operator[](0U); }
 			};
 			using number_type = double;
 			using integer_type = Json::Value::Int;