Keycloak Custom SPI Authenticator - KC-SERVICES0013: Failed authentication - keycloak

Question

Keycloak version 18
Purpose: I want to store scope parameters in user session notes to be later fetched in my custom protocol mapper. To do the same I am referring to this blog post which talks about creating a custom JS authenticator, however, as I prefer Java, I tried implementing the same in java.
I can see the custom authenticator, in my keycloak server-info and during setup.
Here is my implementation:
public class MyAuthenticator implements Authenticator {
private static final Logger log = LoggerFactory.getLogger(MyAuthenticator.class);
#Override
public void authenticate(AuthenticationFlowContext context) {
log.info("authenticate :: START");
try {
AuthenticationSessionModel authenticationSession = context.getAuthenticationSession();
String sessionClientNote = authenticationSession.getClientNote("scope");
log.info("client note from auth session : " + sessionClientNote);
authenticationSession.setUserSessionNote("scope", sessionClientNote);
context.success();
} catch (Exception e) {
context.failureChallenge(AuthenticationFlowError.INTERNAL_ERROR,
context.form().setError("smsAuthSmsNotSent", e.getMessage())
.createErrorPage(Response.Status.INTERNAL_SERVER_ERROR));
}
}
#Override
public void action(AuthenticationFlowContext context) {
log.info("No Custom Action is set.");
context.success();
}
#Override
public boolean requiresUser() {
return true;
}
#Override
public boolean configuredFor(KeycloakSession session, RealmModel realm, UserModel user) {
return true;
}
#Override
public void setRequiredActions(KeycloakSession session, RealmModel realm, UserModel user) {
log.info("No required actions are set.");
}
#Override
public void close() {
}
}
public class MyAuthenticatorFactory implements AuthenticatorFactory {
public static final String PROVIDER_ID = "my-authenticator";
#Override
public String getId() {
return PROVIDER_ID;
}
#Override
public String getDisplayType() {
return "MY Authentication";
}
#Override
public String getHelpText() {
return "Will read the scope parameters and store in user session";
}
#Override
public String getReferenceCategory() {
return PasswordCredentialModel.TYPE;
}
#Override
public boolean isConfigurable() {
return true;
}
#Override
public boolean isUserSetupAllowed() {
return true;
}
#Override
public AuthenticationExecutionModel.Requirement[] getRequirementChoices() {
return REQUIREMENT_CHOICES;
}
#Override
public List<ProviderConfigProperty> getConfigProperties() {
return Collections.emptyList();
}
#Override
public Authenticator create(KeycloakSession session) {
return new MyAuthenticator();
}
#Override
public void init(Config.Scope config) {
}
#Override
public void postInit(KeycloakSessionFactory factory) {
}
#Override
public void close() {
}
}
Here is how the authenticator is set up as the last step as execution :
However, I get this exception while trying to log in or test this via postman. This is not even hitting the custom code that I have written but failing much before that?
2022-08-01 10:52:21,721 WARN [org.keycloak.authentication.DefaultAuthenticationFlow] (executor-thread-25) REQUIRED and ALTERNATIVE elements at same level! Those alternative executions will be ignored: [auth-cookie, identity-provider-redirector, null]
2022-08-01 10:52:21,721 WARN [org.keycloak.services] (executor-thread-25) KC-SERVICES0013: Failed authentication: org.keycloak.authentication.AuthenticationFlowException: authenticator: my-authenticator
at org.keycloak.authentication.DefaultAuthenticationFlow.processSingleFlowExecutionModel(DefaultAuthenticationFlow.java:437)
at org.keycloak.authentication.DefaultAuthenticationFlow.processFlow(DefaultAuthenticationFlow.java:264)
at org.keycloak.authentication.AuthenticationProcessor.authenticateOnly(AuthenticationProcessor.java:1030)
at org.keycloak.authentication.AuthenticationProcessor.authenticate(AuthenticationProcessor.java:892)
And this is the line number. I don't understand this code and what is it trying to do? My is simple authorization code pattern. Can someone please advice/review my code?
I have also set these flows at client level.