It is no longer limited to Azure AD Graph API.
Microsoft Graph API "beta" endpoint now supports creating local and social Azure AD B2C users.
It would look something like:
POST https://graph.microsoft.com/beta/users
{
"accountEnabled": true,
"displayName": "John Smith",
"identities": [
{
"signInType": "emailAddress",
"issuer": "{tenant}.onmicrosoft.com",
"issuerAssignedId": "john.smith@example.com"
}
],
"givenName": "John",
"surname": "Smith"
"passwordProfile": {
"password": "Password123",
"forceChangePasswordNextSignIn": false
},
"passwordPolicies": "DisablePasswordExpiration, DisableStrongPassword"
}
more info here:
link text