In reference to ID Token Structure, this article addresses what an ID Token's Subject (sub) claim contains, its meaning, and the format(s) it can take.

• ID Token
• sub Claim

The Subject (sub) claim is populated with the user’s user_id attribute.  This attribute takes the form of [provider]|[local part]:

• The provider will indicate the strategy being used, such as: auth0, google-oauth2, github, etc
• The local part is flexible in the following ways:
  • It can be explicitly set on account creation
  • If not explicitly set during account creation, it will be a hexadecimal string (for example, 5c6b52fd451bd02197ecbd5f)