I have read the PODIO documentation. I have in particular contemplated the following statement concerning use of the refresh_token:
This request returns the same data as above, and you can continue to
do this over and over again, to keep your application authenticated
without having to ask the user to re-authenticate.
Does this mean that the refresh_token will be indefinitely valid or does it expire:
- X days after being issued; or
- X days after the last use of it for obtaining a new
access_token
EDIT: Please see this PODIO Thread which asks the same questions but does not seem to give any conclusive answers about the PODIO implementation of the Oauth2.0 protocol.
The answer of your question:
Does this mean that the refresh_token will be indefinitely valid or
does it expire?
...can be concluded from the section 1.5 and section 10.4 of the OAuth 2.0 specification.
Section 1.5 Introduction of refresh_token states:
Refresh tokens are issued to the client by the authorization server
and are used to obtain a new access token when the current access
token becomes invalid or expires, or to obtain additional access
tokens with identical or narrower scope (access tokens may have a
shorter lifetime and fewer permissions than authorized by the
resource owner)
section 10.4 Security Considerations for refresh_token states:
The authorization server MUST verify the binding between the refresh
token and client identity whenever the client identity can be
authenticated. When client authentication is not possible, the
authorization server SHOULD deploy other means to detect refresh token
abuse.
For example, the authorization server could employ refresh token
rotation in which a new refresh token is issued with every access
token refresh response. The previous refresh token is invalidated but
retained by the authorization server. If a refresh token is
compromised and subsequently used by both the attacker and the
legitimate client, one of them will present an invalidated refresh
token, which will inform the authorization server of the breach.
It can be concluded that if the authorization_server is able to verify the binding between a refresh_token and the client to whom it was issued then refresh_token can be used to obtain multiple access_token and will never expire. else the authorization sever will invalidate the old refresh_token and generate new refresh_token with every access token refresh response.
Refresh tokens will expire X days (or hours) after their creation. Depending on your security requirements this expiration will be 1 month or 1 hour.
You have to make the decision taking care some aspects as functionality and security.
- If you decide to priorize security, a short expiration could make your application anoying for the user.
- If you decide to priorize functionality, your application could be more vulnerable.
TL; DR
Refresh token will eventually expire or become invalid and you should be ready for it.
Two scenarios:
User facing service (e.g.: authorization grant flow) - maybe ok to ignore the problem, because people are good in turning it off and on again, a.k.a refresh the page :-)
Server side long running service (e.g.: client credentials flow) - you should be ready for the situation when neither of access or refresh token works and re-initiate the authentication from scratch.
Real life
Refresh tokens may or may not have expiry time, depending on your provider they expire never, not as long as they're recently used, in months or in hours. Relying on the fact that you will receive new refresh token with refreshed access token may be tricky.
Timeout is not the only way in which token may become invalid. Consider following scenarios described in oauth0:
While refresh tokens are often long-lived, the authorization server
can invalidate them. Some of the reasons a refresh token may no longer
be valid include:
- the authorization server has revoked the refresh token the user has
- revoked their consent for authorization the refresh token has expired
- the authentication policy for the resource has changed (e.g.,
originally the resource only used usernames and passwords, but now it
requires MFA)
To add to that the tokens (access, refresh) can be stored in non-persistent storage in authentication provider service so if the service is restarted (crash, update) your tokens may be gone.
Conclusion
If you are writing long-running service which needs to be reliable don't rely on being able to refresh granted authentication forever through refresh tokens.
