Oauth2 Password, register and reset password unsopported, why?

### Issue type

**I'm submitting a ...** (check one with "x")

* [ ] bug report
* [ ] feature request
* [x] question

### Issue description

**Current behavior:**
I had configured my Auth strategies as Oauth2 Password, but why it not support register, reset-password and request-password?

**Steps to reproduce:**

**Related code:**

My Oauth2 strategies in core.module:
```
strategies: [
NbOAuth2AuthStrategy.setup({
name: 'password',
clientId: '5',
clientSecret: 'blablabla',
clientAuthMethod: NbOAuth2ClientAuthMethod.BASIC,
baseEndpoint: environment.baseUrlOAuth,
token: {
endpoint: '/token',
grantType: NbOAuth2GrantType.PASSWORD,
class: NbAuthOAuth2JWTToken,
scope: '*',
},
refresh: {
endpoint: '/refresh-token',
grantType: NbOAuth2GrantType.REFRESH_TOKEN,
},
}),
],
forms: {
login: {
redirectDelay: 0,
strategy: 'password',
rememberMe: false,
showMessages: {
success: true,
error: true,
},
},
register: {
redirectDelay: 0,
strategy: 'password',
endpoint: '/auth/signup',
method: 'post',
showMessages: {
success: true,
error: true,
},
terms: true,
},
requestPassword: {
redirectDelay: 0,
strategy: 'password',
endpoint: '/password/create',
method: 'post',
showMessages: {
success: true,
error: true,
},
},
resetPassword: {
redirectDelay: 0,
strategy: 'password',
endpoint: '/password/reset',
method: 'get',
showMessages: {
success: true,
error: true,
},
},
logout: {
redirectDelay: 0,
strategy: 'password',
endpoint: '/auth/logout',
method: 'get',
redirect: {
success: '/auth/login',
failure: '/auth/login',
},
}
```
Error while confirm registration for example: `register is not supported by NbOAuth2AuthStrategy, use authenticate`.

What does "use authenticate" mean?

### Other information:

**npm, node, OS, Browser**
```

Node, npm: `10.13` and `6.19.0`
OS :Centos7
Browser: Chrome

```

**Angular, Nebular**
```
Angular 7
Nebular 4
```