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Make the unlock URL idempotent #5490

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The path GET /resource/unlock?unlock_token=TOKEN is not currently
idempotent, which brings some problems when the page is hit by an
antivirus, prefetch, or anything other than the user. For example,
Microsoft SafeLinks technology visits URLs sent in emails to make sure
that the URL doesn't have malware.

This change keeps, when configured, the unlock token after the resource
has been unlocked. If the user happens to click on the unlock link after
it has already been visited, it will behave as if this was the first
visit, even though the resource is technically unlocked since the first
visit. This makes the GET request idempotent and doesn't break the
current behavior.

This may add a side effect on database queries that check how many
resources have unlock_token not null to count how many resources are
unlocked. To address this side effect, the new behavior is turned off by
default.

The first version of the Lockable module logged the user in, but this
is not true since #1493 was merged. When a resource is locked again,
another unlock token is created and overwrites the older one. Keeping
the most recent unlock token, then, doesn't represent a security issue.

By default, Devise clears the locked_at, failed_attempts and
unlock_token when unlocking a resource. Even though the unlock token
doesn't have an impact on whether a resource is locked or not, such a
change can impact users who depend on this column being not empty. To
address this problem, I'm introducing the new behavior of not cleaning
the unlock token as a opt-in setting.
The path GET /resource/unlock?unlock_token=TOKEN is not currently
idempotent, which brings some problems when the page is hit by an
antivirus, prefetch or anything other than the user. For example,
Microsoft SafeLinks technology visits URLs sent in emails to make sure
that the URL doesn't have malware.

This change keeps, when configured, the unlock token after the resource
has been unlocked. If the user happens to click on the unlock link after
it has already been visited, it will behave as if this was the first
visit, even though the resource is technically unlocked since the first
visit. This makes the GET request idempotent and doesn't break the
current behavior.

This may add a side effect on database queries that check how many
resources have unlock_token not null to count how many resources are
unlocked. To address this side effect, the new behavior is turned off by
default.

The [first version] of the Lockable module logged the user in, but this
is not true since heartcombo#1493 was merged. When a resource is locked again,
another unlock token is created and overwrites the older one. Keeping
the most recent unlock token, then, doesn't represent a security issue.

[first version]:
heartcombo@d2fa737
@neilvcarvalho neilvcarvalho changed the title Make the unlock URL itempotent Make the unlock URL idempotent May 5, 2022
@neilvcarvalho
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neilvcarvalho commented May 5, 2022

Oh, I noticed a possible security issue: by possessing the unlock token, someone may reset the count of login attempts and try to login indefinitely, as long as the account isn't locked. I'll address this issue.

Edit: solved on a6fafd3

We want to avoid malicious actors who possess the last unlock token of a
user to have a way to be able to reset the number of failed attempts
just by visiting the unlock URL.

By early returning `true` on the `unlock_access!` method if the
`locked_at` is blank - i.e. the resource is not locked -, Devise can
behave as if the lock was removed without resetting the failed login
attempts.
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