docs(sdk): identifier is actually required

[aeneasr]

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I am following the contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security. vulnerability,
  I confirm that I got green light (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Merging #2593 (05361e9) into master (f43396b) will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2593      +/-   ##
==========================================
+ Coverage   75.14%   75.21%   +0.06%     
==========================================
  Files         295      295              
  Lines       16361    16361              
==========================================
+ Hits        12295    12306      +11     
+ Misses       3127     3117      -10     
+ Partials      939      938       -1     

Impacted Files	Coverage Δ
selfservice/strategy/webauthn/login.go	62.50% <ø> (ø)
session/test/persistence.go	100.00% <0.00%> (+1.38%)	⬆️
cmd/courier/watch.go	76.27% <0.00%> (+11.86%)	⬆️

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