Add padded base64url payload string

jwt_verify_lib/jwt.h

@@ -44,7 +44,11 @@ struct Jwt {
   // payload string
   std::string payload_str_;
   // payload base64_url encoded
+  // This is the original encoded payload parsed from `jwt_` and should be the one
+  // used in the jwt verification.
   std::string payload_str_base64url_;
+  // payload base64_url encoded with padding
+  std::string payload_str_base64url_padded_;
   // payload in Struct protobuf
   ::google::protobuf::Struct payload_pb_;
   // signature string

src/jwt.cc

@@ -93,6 +93,13 @@ Status Jwt::parseFromString(const std::string& jwt) {
     return Status::JwtPayloadParseErrorBadBase64;
   }
 
+  payload_str_base64url_padded_ = payload_str_base64url_;
+  if (payload_str_base64url_padded_.length() % 4 != 0) {
+    std::string trailing_padding(4 - payload_str_base64url_padded_.length() % 4,
+                                 '=');
+    payload_str_base64url_padded_.append(trailing_padding);
+  }
+
   const auto payload_status = ::google::protobuf::util::JsonStringToMessage(
       payload_str_, &payload_pb_, options);
   if (!payload_status.ok()) {

test/jwt_test.cc

@@ -15,6 +15,7 @@
 #include "jwt_verify_lib/jwt.h"
 
 #include "google/protobuf/util/message_differencer.h"
+#include "absl/strings/escaping.h"
 #include "gtest/gtest.h"
 #include "jwt_verify_lib/struct_utils.h"
 
@@ -69,6 +70,79 @@ TEST(JwtParseTest, GoodJwt) {
   EXPECT_EQ(int_value, 1234);
 }
 
+
+TEST(JwtParseTest, PayloadStrBase64UrlPadded) {
+  struct PayloadStrBase64UrlTestCases {
+    std::string jwt, payload_str_base64url, payload_str_base64url_padded;
+  };
+
+  // For base64 encoding, there are only three length to test"
+  // - 3n bytes => 4n bytes, no padding needed
+  // - 3n + 1 bytes => 4n + 2 bytes, 2 padding needed
+  // - 3n + 2 bytes => 4n + 3 bytes, 1 padding needed
+  PayloadStrBase64UrlTestCases testCases[3] = {
+      // Payload text(3n bytes):
+      // {
+      //   "sub": "1234567890",
+      //   "name": "John Do",
+      //   "iat": 1516239022
+      // }
+      {"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9."
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG8iLCJpYXQiOjE1MTYyMzkwMjJ"
+       "9.9twuPVu9Wj3PBneGw1ctrf3knr7RX12v-UwocfLhXIs",
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG8iLCJpYXQiOjE1MTYyMzkwMjJ"
+       "9",
+       // No padding added.
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG8iLCJpYXQiOjE1MTYyMzkwMjJ"
+       "9"},
+      // Payload text(3n + 1 bytes):
+      // {
+      //   "sub": "1234567890",
+      //   "name": "John Doe",
+      //   "iat": 1516239022
+      // }
+      {"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9."
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDI"
+       "y"
+       "fQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c",
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2"
+       "MjM5MDIyfQ",
+       // 2 padding added.
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2"
+       "MjM5MDIyfQ=="},
+      // Payload text(3n + 2 bytes):
+      // {
+      //   "sub": "1234567890",
+      //   "name": "John Doee",
+      //   "iat": 1516239022
+      // }
+      {"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9."
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lZSIsImlhdCI6MTUxNjIzOTA"
+       "y"
+       "Mn0.1UeFWsD4eTCfiDfgrzySimOvCkKln7pwjQIV5fe4A1Y",
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lZSIsImlhdCI6MTUx"
+       "NjIzOTAyMn0",
+       // 1 padding added.
+       "eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lZSIsImlhdCI6MTUx"
+       "NjIzOTAyMn0="}};
+  for (int i = 0; i < 3; i++) {
+    struct PayloadStrBase64UrlTestCases& tc = testCases[i];
+
+    Jwt jwt;
+    ASSERT_EQ(jwt.parseFromString(tc.jwt), Status::Ok);
+
+    EXPECT_EQ(jwt.payload_str_base64url_, tc.payload_str_base64url);
+    EXPECT_EQ(jwt.payload_str_base64url_padded_,
+              tc.payload_str_base64url_padded);
+
+    std::string decoded_payload_from_padded_str;
+    EXPECT_TRUE(absl::WebSafeBase64Unescape(jwt.payload_str_base64url_padded_,
+                                            &decoded_payload_from_padded_str));
+
+    EXPECT_EQ(decoded_payload_from_padded_str, jwt.payload_str_);
+  }
+}
+
 TEST(JwtParseTest, Copy) {
   Jwt original;
   ASSERT_EQ(original.parseFromString(good_jwt), Status::Ok);