How to make a oauth2 authentication within a spring boot shell application

I'm writing a spring boot shell application which should access a rest API which is protected by keycloak. In a web application is everything fine. The browser redirects me to keycloak and keycloak back to my application and voilà I'm authenticated.

But in Cli/Shell application without browser it seems to be impossible.

All I want is to get an access token to attach it to each rest request. Like this:

POST {{realmUri}}/protocol/openid-connect/token 
Content-Type: application/x-www-form-urlencoded
Accept: application/json

grant_type=password
&username={{username}}
&password={{userPassword}}
&client_id={{clientId}}
&client_secret={{clientSecret}}
&scope=openid+phone

That returns the access token. How can I achieve this via spring security oauth. The "Resource Owner Password Flow" should be the right thing but it is not inplemented.

But I think it must be possible.

Maybe OAuth2LoginAuthenticationProvider could do the job.

That's my final solution:

@Service
@Slf4j
@RequiredArgsConstructor
public class TokenService {

    private OAuth2User currentUser;

    @Getter
    @Setter
    @ToString
    public static class OAuth2AccessTokenResponse {
        @JsonProperty(OAuth2ParameterNames.ACCESS_TOKEN)
        private String accessToken;

        @JsonProperty(OAuth2ParameterNames.EXPIRES_IN)
        private String expiresIn;

        @JsonProperty("refresh_expires_in")
        private String refreshExpiresIn;

        @JsonProperty(OAuth2ParameterNames.REFRESH_TOKEN)
        private String refreshToken;

        @JsonProperty(OAuth2ParameterNames.TOKEN_TYPE)
        private String tokenType;

        @JsonProperty("not-before-policy")
        private String notBeforePolicy;

        @JsonProperty("session_state")
        private String sessionState;

        @JsonProperty(OAuth2ParameterNames.SCOPE)
        private String scope;
    }

    @Data
    @Builder
    @RequiredArgsConstructor
    public static class OAuth2User {
        private final Jwt accessToken;
        private final OAuth2AccessTokenResponse response;

        public String getRefreshToken() {
            return response.refreshToken;
        }
    }

    private final OAuth2ClientProperties tokenServiceProperties;
    private final RestTemplate simpleRestTemplate = new RestTemplateBuilder().build();;

    protected OAuth2User resposeToUser(OAuth2AccessTokenResponse response) {
        var jwtDecoder = JwtDecoders
                .fromIssuerLocation(tokenServiceProperties.getProvider().get("keycloak").getIssuerUri());
        Jwt accessToken = jwtDecoder.decode(response.getAccessToken());
        return OAuth2User.builder().accessToken(accessToken).response(response).build();
    }

    public OAuth2User authenticateUser(String username, String password) {
        log.info("Try to login user {}", username);
        var token = sendUserAuthenticationRequest(username, password);
        log.debug("User {} successfully log in {}", username, token);
        currentUser = token;
        return currentUser;
    }

    OAuth2User sendUserAuthenticationRequest(String username, String password) {
        MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
        map.add("grant_type", "password");
        map.add("client_id", tokenServiceProperties.getRegistration().get("keycloak").getClientId());
        map.add("username", username);
        map.add("password", password);
        var token = sendKeycloakRequest(map);
        return resposeToUser(token);
    }

    OAuth2User sendTokenRefreshRequest(String refreshToken) {
        MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
        map.add("grant_type", "refresh_token");
        map.add("client_id", tokenServiceProperties.getRegistration().get("keycloak").getClientId());
        map.add("refresh_token", refreshToken);
        var token = sendKeycloakRequest(map);
        return resposeToUser(token);
    }

    OAuth2AccessTokenResponse sendKeycloakRequest(MultiValueMap<String, String> map) {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
        headers.setAccept(Collections.singletonList(MediaType.APPLICATION_JSON));

        HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, headers);
        ResponseEntity<OAuth2AccessTokenResponse> exchange = simpleRestTemplate.exchange(
                tokenServiceProperties.getProvider().get("keycloak").getTokenUri(), HttpMethod.POST, request,
                OAuth2AccessTokenResponse.class);
        return exchange.getBody();
    }

    public String getAccessToken() {
        if (currentUser == null) {
            throw new CliException(ErrorCode.user_not_logged_in);
        }
        if (currentUser.accessToken.getExpiresAt().isBefore(Instant.now())) {
            log.info("Refresh token {}", currentUser.accessToken);
            currentUser = sendTokenRefreshRequest(currentUser.getRefreshToken());
        }
        return currentUser.accessToken.getTokenValue();
    }

}