Why is Spring telling me the controller is an unknown entity upon saving a user?

After a few hours of running against the wall with this code, I’ve just about had it. This error is as indescriptive as can be.

My User entity:

https://pastebin.com/fqRJmMCc

package cc.serviceops.account;
import cc.serviceops.account.helpers.UserRole;
import cc.serviceops.organisation.Organisation;
import cc.serviceops.organisation.Team;
import cc.serviceops.ticket.Ticket;
import cc.serviceops.ticket.TicketAction;
import lombok.Getter;
import lombok.Setter;
import org.springframework.lang.Nullable;
import javax.persistence.*;
import java.util.Objects;
import java.util.List;

@Entity @Table(name = "account")
@Getter @Setter
public class User {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    private String password;
    private String email;

    @Column(name ="first_name", nullable = true)
    private String firstName;

    @Column(name ="last_name", nullable = true)
    private String lastName;

    @Nullable
    private String telephone;

    private boolean enabled = true;

    @Enumerated(EnumType.STRING)
    private UserRole role = UserRole.GUEST;

    @ManyToOne(optional = true) @JoinColumn(name = "team_id")
    private Team team;

    @ManyToOne(optional = true) @JoinColumn(name = "organisation_id")
    private Organisation organisation;

    @OneToMany(mappedBy = "user")
    private List<Ticket> ticketList;

    @OneToMany(mappedBy = "creator")
    private List<Ticket> createdTicketList;

    @OneToMany(mappedBy = "user")
    private  List<TicketAction> actionList;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        User user = (User) o;
        return id == user.id;
    }

    @Override
    public int hashCode() {
        return Objects.hash(id);
    }
}

TicketController controller with just the function that holds user info:

https://pastebin.com/n7jeciAM

package cc.serviceops.ticket;
import cc.serviceops.Tools;
import cc.serviceops.account.User;
import cc.serviceops.account.dao.SignupService;
import cc.serviceops.account.dao.UserService;
import cc.serviceops.organisation.Organisation;
import cc.serviceops.organisation.dao.OrganisationService;
import cc.serviceops.organisation.Team;
import cc.serviceops.ticket.dao.TicketService;
import cc.serviceops.ticket.helpers.*;
import lombok.AllArgsConstructor;
import org.springframework.http.HttpStatus;
import org.springframework.security.access.prepost.PreAuthorize;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.server.ResponseStatusException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.validation.Valid;
import java.security.Principal;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.util.*;
import java.util.stream.Collectors;

@Controller @AllArgsConstructor
public class TicketController {
    private final UserService userService;
    private final OrganisationService organisationService;
    private final TicketService ticketService;
    private final SignupService signupService;

    @GetMapping("/{organisation:^(?!css$|scripts$|img$|fonts$).*}/{ticket}")
    public String showTicket(@PathVariable("organisation") String organisationName,
                             @PathVariable("ticket") String ticketId,
                             Model model, Principal principal) {
...
        if (principal == null) {
            model.addAttribute("anonymousTicketDto", getAnonymousDtoFromTicket(ticket));
            return "ticket/anonymous";
        }

        model.addAttribute("ticketDto", getDtoFromTicket(ticket));
        return "ticket/ticket";
    }
...
    @PostMapping("/{organisation:^(?!css$|scripts$|img$|fonts$).*}/anonymous")
    public String doTicket(@Valid @ModelAttribute AnonymousTicketDto anonymousTicketDto, BindingResult bindingResult,
                           @PathVariable("organisation") String organisationName, Model model,
                           HttpServletRequest request) {
        Organisation activeOrganisation = organisationService.getOrganisationByName(organisationName);
        User activeUser = userService.getByEmail(anonymousTicketDto.getCreatorEmail());

        if (activeOrganisation == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Organisation cannot be found");
        }

        if (anonymousTicketDto.getCategory() == null || anonymousTicketDto.getCategory().getId() < 1) {
            bindingResult.rejectValue("category.id", "ticket.category");
        }

        if (activeUser != null) {
            bindingResult.rejectValue("creatorEmail", "user.email.duplicate");
        }

        if (!anonymousTicketDto.getPassword().equals(anonymousTicketDto.getPasswordConfirmation()) &&
                !anonymousTicketDto.getPasswordConfirmation().isBlank()) {
            bindingResult.rejectValue("passwordConfirmation", "user.password.confirmation");
        }

        if (bindingResult.hasErrors()) {
            fillTicketAttributes(activeOrganisation, model);
            model.addAttribute("anonymousTicketDto", anonymousTicketDto);
            return "ticket/anonymous";
        }

        activeUser = new User() {{
            setEmail(anonymousTicketDto.getCreatorEmail());
            setPassword(anonymousTicketDto.getPassword());
        }};

        activeUser = signupService.saveGuest(activeUser);
        // Password in activeUser is encrypted
        authWithHttpServletRequest(request, activeUser.getEmail(), anonymousTicketDto.getPassword());
        Ticket ticket = getTicketFromDto(anonymousTicketDto);
        ticket.setCreator(activeUser);
        ticket = ticketService.saveTicket(ticket);
        return String.format("redirect:/%s/%s?success", organisationName, ticket.getId());
    }
...
}

User service and repository essentials:

https://pastebin.com/acYUF7sN

package cc.serviceops.account.dao;
import cc.serviceops.account.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import java.util.List;

public interface UserRepository extends JpaRepository<User, Integer> {}

=================
other file
=================
@Override
public User saveGuest(User user) {
    String password = passwordEncoder.encode(user.getPassword());
    user.setPassword(password);
    return userRepository.save(user);
}

Long story short is that the User object should only need a mail address, password and “enabled” field, which is by default true. Yet, for some reason when this bare minimum of info is passed to the database to make a user, I get an error saying TicketController is an “unknown entity”. Even though TicketController shouldn’t have anything to do with the database:

2021-09-17 21:08:28.134 ERROR 53256 --- [nio-8080-exec-7] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.InvalidDataAccessApiUsageException: Unknown entity: cc.serviceops.ticket.TicketController$2; nested exception is java.lang.IllegalArgumentException: Unknown entity: cc.serviceops.ticket.TicketController$2] with root cause

java.lang.IllegalArgumentException: Unknown entity: cc.serviceops.ticket.TicketController$2
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:723) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:706) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:362) ~[spring-orm-5.3.9.jar:5.3.9]
    at com.sun.proxy.$Proxy102.persist(Unknown Source) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:311) ~[spring-orm-5.3.9.jar:5.3.9]
    at com.sun.proxy.$Proxy102.persist(Unknown Source) ~[na:na]
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:597) ~[spring-data-jpa-2.5.3.jar:2.5.3]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker$RepositoryFragmentMethodInvoker.lambda$new$0(RepositoryMethodInvoker.java:289) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryComposition$RepositoryFragments.invoke(RepositoryComposition.java:529) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryComposition.invoke(RepositoryComposition.java:285) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$ImplementationMethodExecutionInterceptor.invoke(RepositoryFactorySupport.java:599) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:163) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:138) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:80) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:174) ~[spring-data-jpa-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.9.jar:5.3.9]
    at com.sun.proxy.$Proxy108.save(Unknown Source) ~[na:na]
    at cc.serviceops.account.dao.SignupServiceImpl.saveGuest(SignupServiceImpl.java:71) ~[classes/:na]
    at cc.serviceops.ticket.TicketController.doTicket(TicketController.java:279) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1064) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:681) ~[tomcat-embed-core-9.0.50.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.9.jar:5.3.9]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[tomcat-embed-core-9.0.50.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:228) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:327) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:115) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:81) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:121) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:115) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:126) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:81) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:105) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:133) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:92) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:149) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:218) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:212) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:103) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:89) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:132) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:110) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:80) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:55) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:211) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:183) ~[spring-security-web-5.5.1.jar:5.5.1]
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271) ~[spring-web-5.3.9.jar:5.3.9]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.9.jar:5.3.9]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.9.jar:5.3.9]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:190) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:163) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1723) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.50.jar:9.0.50]
    at java.base/java.lang.Thread.run(Thread.java:829) ~[na:na]

2021-09-17 21:08:28.140  WARN 53256 --- [nio-8080-exec-7] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.web.HttpRequestMethodNotSupportedException: Request method 'POST' not supported]

SignupServiceImpl:

pastebin.com/D1TmHUWp 

@SpringBootApplication starter:

https://pastebin.com/bHFwMEnx

TicketController has a @Controller annotation, User has an @Entity, SignupServiceImpl has a @Service and still it complains about TicketController not being a known entity…

Config: pom: pastebin.com/B4EeKkmz application config: pastebin.com/KuCndSVY db config class: pastebin.com/FigJScit security config class: pastebin.com/CuAxRErX web config class: pastebin.com/qAHFY3jW

Answer

I think the reason is that you are creating an anonymous class in your code.

 activeUser = new User() {{
        setEmail(anonymousTicketDto.getCreatorEmail());
        setPassword(anonymousTicketDto.getPassword());
    }};

needs to be something like

 activeUser = new User();
 activeUser.setEmail(anonymousTicketDto.getCreatorEmail());
 activeUser.setPassword(anonymousTicketDto.getPassword());

Some Background Information about anonymous classes in Java: https://www.baeldung.com/java-anonymous-classes

A cool tool that might ease the transformation between DTO and Entity in the Controller (I personally use it in some projects and really like it): https://mapstruct.org/