Fix a lot of things about sharing

[nono]

No description provided.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@5e936a3). Click here to learn what that means.
The diff coverage is 39.76%.

@@            Coverage Diff            @@
##             master    #1130   +/-   ##
=========================================
  Coverage          ?   85.17%           
=========================================
  Files             ?      175           
  Lines             ?    52193           
  Branches          ?        0           
=========================================
  Hits              ?    44456           
  Misses            ?     6305           
  Partials          ?     1432

Impacted Files	Coverage Δ
pkg/sharings/member.go	72.28% <ø> (ø)
pkg/workers/sharings/sharing_updates.go	25.54% <0%> (ø)
web/sharings/sharings.go	70% <0%> (ø)
pkg/sharings/workflow.go	23.97% <0%> (ø)
web/auth/auth.go	60.03% <0%> (ø)
pkg/sharings/sharings.go	78.89% <100%> (ø)
pkg/sharings/revoke.go	62.79% <45.45%> (ø)
pkg/workers/mails/mail_templates.go	93.57% <50%> (ø)
web/permissions/permissions.go	73% <50%> (ø)
pkg/permissions/permissions.go	72.07% <57.14%> (ø)
... and 2 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5e936a3...b7b2a35. Read the comment docs.

[enguerran]

There is a lot of code duplication

if perm.Expired() {
    return nil, ErrExpiredToken
}
return perm, nil

[jinroh]

Why not using a *time.Time ?

[nono]

Good question. I have copied what was done here: https://github.com/cozy/cozy-stack/blob/master/pkg/oauth/client.go#L63