[keycloak-user] JWT - Base64 encode/decode issues

[Fabricio Milone]

Hi everyone,

I've been experiencing some random issues when trying to decode the
returned idToken from the /protocol/openid-connect/token call.

I've found that sometimes the returned idToken is not multiple of 4 and has
no padding at the end of the payload section (where mappers are added). So
the result is that I'm losing the last 2 characters of the last mapper
value.

This is one example of a failing token (payload only):

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


787 chars (should be 788)

if you try to decode it, you'll get:

{"jti":"85ce8eee-47f9-4393-878b-b24b504ab31f","exp":1462766723,"nbf":0,"iat":1462766423,"iss":"
> https://idm-s2.sb.dev.sbetenv.com/auth/realms/electricsheep","aud":"es","sub":"03edc374-c820-4d1a-ba7f-3f479f8db2c8","typ":"ID","azp":"es","session_state":"1cb4297f-8807-48ee-80a5-a12974a7a2bd","name":"fname
> lname","custId":"2567581","preferred_username":"anthtest","given_name":"fname","family_name":"lname","email":"
> noboday at sportsbet.com.au
> ","token":"k8gsZ+9lWGeeEhomvwOhpY9myfywNB/BXMFYpDB1+e7GDBQkHuGPRb2G8N1b1Qw2rPwNV+oM2sQILUYWau/HqEgrVQXFxgPwgSUyzQKqhF2uoJ7rsLRdHW3kvQG/I1G5ZQmFygDMokcT


Which is incomplete. The last two chars (which are *"}*) are missing at the
end.

So now, if I take the correct complete json and try to encode using another
library (as the one used here: https://www.base64encode.org/), I'll get:

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
> *=*


(788 chars, which is ok)

Note the equal sign at the end.

I'm wondering why Keycloak is not adding those paddings, is that a bug on
the lib you are using to encode the payload?

As for now, I'm using a workaround that checks for the length of the token
and adds the missing padding when needed before try to decode it.

while (payload.length() % 4 != 0) payload += "=";


That works but it is not ideal.

*Should I create a bug on Keycloak's issue tracker?*

Thanks in advance.

Regards,
Fab
-- 
*Fabricio Milone*
Developer

*Shine Consulting *

30/600 Bourke Street

Melbourne VIC 3000

T: 03 8488 9939

M: 04 3200 4006


www.shinetech.com  *a* passion for excellence
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