B4J Code Snippet [B4X] Get JWT Payload (JavaWebToken)

This function reads the payload of a jwt token and returns a map

Input token:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJjb2xsZWN0aW9uSWQiOiJfcGJfdXNlcnNfYXV0aF8iLCJleHAiOjE3Mzc4NDc5MjksImlkIjoiNzA4MXNoeDM3YzY3dmUzIiwicmVmcmVzaGFibGUiOnRydWUsInR5cGUiOiJhdXRoIn0.W0ZA6c2_qKhbjjvnUKDJPfO-kU-_prk235_YU8fYBxU

Payload from this token:

Public Sub GetJWTPayload(Token As String) As Map
    Dim su As StringUtils
    Dim parts() As String = Regex.Split("\.", Token)
    Dim ResultMap As Map
    ResultMap.Initialize
    
    Dim b() As Byte = su.DecodeBase64(IIf(parts(1).Contains("="),parts(1),parts(1) & "="))
    ResultMap.Put("Payload",BytesToString(b, 0, b.Length, "UTF-8").As(JSON).ToMap)
    
    Return ResultMap
End Sub

 

[aeric]

IIf(parts(1).Contains("="),parts(1),parts(1) & "=")

Is this part necessary?

 

[Alexander Stolte]

Is this part necessary?

I have currently only tested the code in B4J, but if I leave out the “=” character, then a piece of the json string is missing after decoding.

 

[aeric]

I tried to decode my JWT token with your function but failed.
Asking Gemini, I found the fix.

Understanding Base64 Padding
In Base64 encoding, padding with equal signs ("=") is crucial. Here's why:

• Grouping: Base64 encodes data in groups of 3 bytes. Each group is then translated into 4 characters.
• Padding's Role: If the original data isn't a multiple of 3 bytes, padding is added to ensure the final encoded string is a multiple of 4 characters.

Manual Padding Steps

1. Determine Padding Length:
   • Calculate the length of the encoded string modulo 4.
   • If the result is 0, no padding is needed.
   • If the result is 2, add "==".
   • If the result is 3, add "=".
2. Add Padding:
   • Append the appropriate number of "=" signs to the end of the encoded string.

Here is my code:

Public Sub GetJWTPayload (Token As String) As Map
    Dim parts() As String = Regex.Split("\.", Token)
    Dim encoded As String = parts(1)
    Select encoded.Length Mod 4
        Case 2
            encoded = encoded & "=="
        Case 3
            encoded = encoded & "="
    End Select
    Dim su As StringUtils
    Dim b() As Byte = su.DecodeBase64(encoded)
    Dim payload As String = BytesToString(b, 0, b.Length, "UTF-8")
    Return payload.As(JSON).ToMap
End Sub

 

[Mashiane]

@Alexander Stolte , I see the journey to AS B4xPocketBase has started...

 

[Alexander Stolte]

I see the journey to AS B4xPocketBase has started...

He got me ^^
I've already finished the Auth module, I'm currently working on the CRUD. There are clear differences to Supabase

 

[aeric]

AS B4xPocketBase

Sorry for out of topic, what's the difference between Alex and Mashiane versions?

 

[Mashiane]

Sorry for out of topic, what's the difference between Alex and Mashiane versions?

Alex's version can be used with b4x frameworks using httpUtils (native apps), mine only works with BANano via fetch api (web)