Create function to decode and verify.

README.md

@@ -7,7 +7,7 @@ A JWT implementation in Classic ASP, currently only supports `JWTEncode(dictiona
 ```asp
 <!--#include file="jwt.asp" -->
 <%
-Dim sKey, dAttributes, sToken
+Dim sKey, dAttributes, sToken, decodedPayload, isValidJWT
 
 sKey = "Shared Secret"
 Set dAttributes=Server.CreateObject("Scripting.Dictionary")
@@ -19,6 +19,12 @@ dAttributes.Add "name", "Roger"
 dAttributes.Add "email", "[email protected]"
 
 sToken = JWTEncode(dAttributes, sKey)
+
+' Decode JWT token string and get payload. (WARNING : Not verify)
+decodedPayload = JWTDecode(sToken)
+
+' Verify JWT String. (Returns Boolean)
+isValidJWT = JWTVerify(sToken, sKey)
 %>
 ```
 

jwt.asp

@@ -6,7 +6,12 @@ Function JWTEncode(dPayload, sSecret)
   Dim sPayload, sHeader, sBase64Payload, sBase64Header
   Dim sSignature, sToken
 
-  sPayload = DictionaryToJSONString(dPayload)
+  If Typename(dPayload) = "Dictionary" Then
+    sPayload = DictionaryToJSONString(dPayload)
+  Else
+    sPayload = dPayload
+  End If
+
   sHeader  = JWTHeaderDictionary()
 
   sBase64Payload = SafeBase64Encode(sPayload)
@@ -42,4 +47,26 @@ Function JWTHeaderDictionary()
 
   JWTHeaderDictionary = DictionaryToJSONString(dOut)
 End Function
+
+' Returns decoded payload (not verify)
+Function JWTDecode(token)
+    Dim tokenSplited, sPayload
+    tokenSplited = Split(token, ".")
+    If UBound(tokenSplited) <> 2 Then
+        JWTDecode = "Invalid token"
+    Else
+        sPayload = tokenSplited(1)
+        sPayload = SafeBase64ToBase64(sPayload)
+        JWTDecode = Base64Decode(sPayload)
+    End If
+End Function
+
+' Returns if token is valid
+Function JWTVerify(token, sKey)
+    Dim jsonPayload, reEncodingToken, tokenPayload
+    tokenPayload = JWTDecode(token)
+    reEncodingToken = JWTEncode(tokenPayload, sKey)
+
+    JWTVerify = (token = reEncodingToken)
+End Function
 %>

utils.asp

@@ -24,6 +24,17 @@ Function Base64ToSafeBase64(sIn)
   Base64ToSafeBase64 = sOut
 End Function
 
+' change safe base64 to original base64
+Function SafeBase64ToBase64(sIn)
+    Dim removedEqualityLen
+    removedEqualityLen = 4 - Len(sIn) mod 4
+    If removedEqualityLen = 4 Then removedEqualityLen = 0
+    sOut = Replace(sIn,"-","+")
+    sOut = Replace(sOut,"_","/")
+    sOut = sOut & Replace(Space(removedEqualityLen)," ","=")
+    SafeBase64ToBase64 = sOut
+End Function
+
 ' Converts an ASP dictionary to a JSON string
 Function DictionaryToJSONString(dDictionary)
   Set oJSONpayload = New aspJSON