Fix string view overload for claim value

include/jwt/jwt.hpp

@@ -300,7 +300,9 @@ public: // Exposed APIs
    */
   template <typename T,
             typename=typename std::enable_if_t<
-              !std::is_same<system_time_t, std::decay_t<T>>::value>
+              !std::is_same<system_time_t, std::decay_t<T>>::value ||
+              !std::is_same<jwt::string_view, std::decay_t<T>>::value
+              >
            >
   bool add_claim(const string_view cname, T&& cvalue, bool overwrite=false)
   {
@@ -320,6 +322,13 @@ public: // Exposed APIs
     return true;
   }
 
+  /**
+   */
+  bool add_claim(const string_view cname, const string_view cvalue, bool overwrite=false)
+  {
+    return add_claim(cname, std::string{cvalue.data(), cvalue.length()}, overwrite);
+  }
+
   /**
    */
   bool add_claim(const string_view cname, system_time_t tp, bool overwrite=false)

tests/test_jwt_encode.cc

@@ -155,6 +155,31 @@ TEST (EncodeTest, StrEncodeHS512WithKey)
   EXPECT_EQ (enc_str, expected_sign);
 }
 
+TEST (EncodeTest, StrEncodeChangeAlg)
+{
+  using namespace jwt::params;
+
+  const char* expected_none_sign = 
+    "eyJhbGciOiJOT05FIiwidHlwIjoiSldUIn0.eyJhdWQiOiJyaWZ0LmlvIiwiZXhwIjoxNTEzODYzMzcxLCJzdWIiOiJub3RoaW5nIG11Y2gifQ.";
+
+  jwt::string_view key = "00112233445566778899";
+
+  std::map<std::string, jwt::string_view> p;
+  p["aud"] = "rift.io";
+  p["sub"] = "nothing much";
+
+  jwt::jwt_object obj{algorithm(jwt::algorithm::HS512),
+                      secret(key),
+                      payload(std::move(p))
+                     };
+  obj.add_claim("exp", 1513863371);
+
+  obj.header().algo("none");
+  std::string enc_str = obj.signature();
+
+  EXPECT_EQ (expected_none_sign, enc_str);
+}
+
 int main(int argc, char **argv) 
 {
   ::testing::InitGoogleTest(&argc, argv);