`auth.loginWithUsername`:
```ts
auth: {
loginWithUsername: {
allowEmailLogin: true, // default: false
requireEmail: false, // default: false
}
}
```
#### `allowEmailLogin`
This property will allow you to determine if users should be able to
login with either email or username. If set to `false`, the default
value, then users will only be able to login with usernames when using
the `loginWithUsername` property.
#### `requireEmail`
Require that users also provide emails when using usernames.
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