Generate JWT OAuth2 Access token without password - spring-boot

Question

My Spring Boot authorization service is able to create JWT tokens for users with correct credentials. It shall also be possible to get a token via social login (Facebook in this case).
The Facebook authentication already works and I find myself redirected to the following endpoint after I get the users's Facebook data.
I could create the JWT token completely from scratch, but that is not what I want. I want to use the already configured (with key pair and so on) TokenServices from my authentication server.
The only way I found was via TokenEndpoint. The problem is that I need the user's password, which I don't have and shouldn't have at this point.
How can I generate the token from what I already configured?
This endpoint is where I end up after Facebook's redirect:
#GetMapping("/loginSuccess")
fun getLoginInfo(authentication: OAuth2AuthenticationToken): ResponseEntity<OAuth2AccessToken> {
val client = authorizedClientService.loadAuthorizedClient<OAuth2AuthorizedClient>(authentication.authorizedClientRegistrationId, authentication.name)
val userInfoEndpointUri = client.clientRegistration.providerDetails.userInfoEndpoint.uri
if (!StringUtils.isEmpty(userInfoEndpointUri)) {
val restTemplate = RestTemplate()
val headers = HttpHeaders()
headers.add(HttpHeaders.AUTHORIZATION, "Bearer " + client.accessToken.tokenValue)
val entity = HttpEntity("", headers)
val response = restTemplate.exchange(userInfoEndpointUri, HttpMethod.GET, entity, Map::class.java)
// At this point I have the email address of the user and I am able to
// map it to my own User Entity
// This is where I would like to create a token and return it
// However, the following generation process requires the user's password
return authService.generateToken((response.body as Map<*, *>)["email"] as String)
}
throw AuthenticationException("Error")
}
I would like to use getAccessToken(OAuth2Authentication authentication) in JwtTokenStore but its implementation returns null:
#Override
public OAuth2AccessToken getAccessToken(OAuth2Authentication authentication) {
// We don't want to accidentally issue a token, and we have no way to
// reconstruct the refresh token
return null;
}