Any user is identified using the identify method in the IDSync API using one of the mParticle SDKs or by making a direct call to the IDSync HTTP API, regardless of whether or not the user is anonymous or known.
The SDKs automatically call the identify method when they are initialized (e.g. when a new page of your app is loaded).
The SDKs will pass any available device IDs and existing cookies to mParticle to help identify anonymous users. For known users, the SDK will also pass any available user identities (such as a customer ID, phone number, or email address) to mParticle.
mParticle will then iterate through your account’s identity priority in ascending order looking for the first user profile on record that matches the user identities supplied in the identify call.
If a matching profile is found, then your user has been identified. All future user data will be appended to the found user profile. Any data collected prior to identification will be handled differently according to the identity strategy configured for your account.
If no matching profile is found, then mParticle will add the supplied user identities to the existing user profile being used.