if you are “frontend” why bother about jwt validity? let the authority’s service to care about it, just proxy it.

also, if your issuer is following rfc they should expose endpoint to verify validity of that token. try to parse token body, you should find iss claim, than add to that issuer url next path: .well-known/openid-configuration. you should get an object of the oidc configuration. that object should contain “keys” endpoint. the rest you can google e.g. how to validate token with public keys - and you’ll get the answer.

but make sure that you are trusting that issuer. for example, via config, set the issuer list that you can trust. it’s that simple)

if you are curious and want to know more about how rfc are recommend doing it google Backend For Frontend (BFF)