Standalone verification of Keycloak access-token

I am using Keycloak to handle login and generate JWT tokens. I need to be able to verify the access token that I'm sending to my REST API service. Best practice is to use the JWT secret to verify the token directly rather than send it to the Keycloak server for verification. There are a lot of Java examples of doing this, but I need to be able to verify this using python or ruby.

I tried the following python signature verification but I get an error of ValueError: Could not unserialize key data. I also tried entering the public key in the https://jwt.io debugger but also get an invalid signature.

#!/usr/bin/env python3

import jwt

# Public key from Keycloak realm -> Keys -> Public Key -> (view)
public_key = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAu77nUtVw7SIIcUTSiStzMPB7BGB/9eS+CpppsUaiyZyWCXlrALT3YdqneSlpX4Ta+0wvhOkKQtoSS8dCH8GIi7esAmfdHetHfRgeDXHAlXo8HIzshUzODg3ysT7j+Ha3eJsO+LNS/omHDhsarP8Z2eThW876iKJCCc/mB76a6u1e4Id+52K5lG++m8Pn4Gs+cqd2sKUKcMJ9CkJ6dBIdGlXHMoOHj4C33SPrEG/vEBv5cu0l5PP3RiBAuaZHpLKzfIiaLOpj/k4dD/weVt5gwTIJn16AEgPD7173Xef0HgoPlQInDFrJwsGpYCnIPZWSxRbvjKkya2Auj0QZyMCrXwIDAQAB"

# Keycloak JWT RS256 access-token
access_token = "eyJhbGciOiJSUzI1NiIsInR5cCIgOiAiSldUIiwia2lkIiA6ICI0LVlJOUlVc2R6NGM0SHoycXczT0xXZ0I0eHc2eFd4T29XdktVT2FvV3FzIn0.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.Q7s-qTcJyH69Ebof8pQI1kZzeT8olwQnRJ06uas5TP2isacxOheHnJ9ixEvqTrr-iefmYMwx41jM68NCs6l8IBNHqv7t5-ediizx4ianMiXr7oZ_1oAT9hkLyrpv9iF2IZBtzNJz0GQAnDYe1moLOLuzqwvcUaWgmzRY95xvzo4kbE8OkeZiMpD_cDmp3_vKOsdn3B6ybJ9TXtea55A29pQzsvAM_6lHeyxTCisipOtu_ubnUOamkYSpxLwWZXgI1w7iz-igt-n7xtlFhUpra239yn9uly9iuBtlgnc3TFDmZn-XRq_PODDJNJeaQXDRaDqnRQhXsoObxCaPqXDQ3A"

access_token_json = jwt.decode(access_token, public_key)
print(access_token_json)

Solution

To verify the access token I did the following things:

I reset the expiration timeframe so I didn't have to worry about timeouts as a complicating factor.
I had to add the BEGIN/END header/footer to the pubkey (of which there are two different versions based on the encoding of the pubkey -e.g. 'BEGIN RSA PUBLIC KEY' is not the right version for the Keycloak pubkey encoding):

Last - I had to add the audience='belmgr' to the jwt.decode for the python script

## Python script 
#!/usr/bin/env python3
    
import jwt
    
public_key = """-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAu77nUtVw7SIIcUTSiStzMPB7BGB/9eS+CpppsUaiyZyWCXlrALT3YdqneSlpX4Ta+0wvhOkKQtoSS8dCH8GIi7esAmfdHetHfRgeDXHAlXo8HIzshUzODg3ysT7j+Ha3eJsO+LNS/omHDhsarP8Z2eThW876iKJCCc/mB76a6u1e4Id+52K5lG++m8Pn4Gs+cqd2sKUKcMJ9CkJ6dBIdGlXHMoOHj4C33SPrEG/vEBv5cu0l5PP3RiBAuaZHpLKzfIiaLOpj/k4dD/weVt5gwTIJn16AEgPD7173Xef0HgoPlQInDFrJwsGpYCnIPZWSxRbvjKkya2Auj0QZyMCrXwIDAQAB
-----END PUBLIC KEY-----"""
    
access_token = "eyJhbGciOiJSUzI1NiIsInR5cCIgOiAiSldUIiwia2lkIiA6ICI0LVlJOUlVc2R6NGM0SHoycXczT0xXZ0I0eHc2eFd4T29XdktVT2FvV3FzIn0.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.DfC1c6BVBZ8Bgwu6CYGBsWp4T0dqltwAQ84E1Q0LdjFxvtVeDOF8rBIdgkr7rMCHObZWsEotljSR4BZzCvfDNmdk_25sedvi-ZHXTP0-nSeHczIXBstZ8p257A6-fEiIcG5CRoClHMI317bVGjNkzAV7l8kuBhr0bfrDedxpvKo3EQah4MrOF7-JXQGPAWlLDV1E9zsrT99Vm_XL58M-ur8q7N-B-CmOBV2GGsMEosTDK_-U-mattEN6PMNiG004Ryg0iPDM4-kr1AQsPE_wHBYf81_-vrqs7ec--0ShJYdC8-eBbuf9xVixNQVPRl7mnktaKA19YXdzdCwcQa6crw"
    
access_token_json = jwt.decode(access_token, public_key, audience='belmgr')
print(access_token_json)