No puedo realizar CRUD a través de json POST desde el cliente tranquilo Postman en la tabla compuesta que tiene una columna adicional. Estoy usando Spring boot, spring data rest y spring JPA. Tengo 3 tablas en la base de datos
-usuario
-competencia
-user_competency (tabla de unión / compuesta con columna adicional)

Aqui estan mis clases

Usuario

@Entity
@Table(name = "\"user\"", schema = "public")
@JsonIdentityInfo(
          generator = ObjectIdGenerators.IntSequenceGenerator.class, 
          property = "userId")
public class User implements java.io.Serializable {

    private Long userId;

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)

    @Column(name = "user_id", unique = true, nullable = false)
    public Long getUserId() {
        return this.userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }

    private Set<UserCompetency> userCompetencies = new HashSet<UserCompetency>(0);

        @OneToMany(fetch = FetchType.EAGER,cascade = {CascadeType.ALL}, mappedBy = "user")
    public Set<UserCompetency> getUserCompetencies() {
        return this.userCompetencies;
    }

    public void setUserCompetencies(Set<UserCompetency> userCompetencies) {
        this.userCompetencies = userCompetencies;
    }

}

Competencia

@Entity
@Table(name = "competency", schema = "public")
@JsonIdentityInfo(
          generator = ObjectIdGenerators.IntSequenceGenerator.class, 
          property = "competencyId")
public class Competency implements java.io.Serializable {


    private Long competencyId;
    private Set<UserCompetency> userCompetencies = new HashSet<UserCompetency>(0);

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)

    @Column(name = "competency_id", unique = true, nullable = false)
    public Long getCompetencyId() {
        return this.competencyId;
    }

    public void setCompetencyId(Long competencyId) {
        this.competencyId = competencyId;
    }

        @OneToMany(fetch = FetchType.LAZY, mappedBy = "competency")
    public Set<UserCompetency> getUserCompetencies() {
        return this.userCompetencies;
    }

    public void setUserCompetencies(Set<UserCompetency> userCompetencies) {
        this.userCompetencies = userCompetencies;
    }
}   

UserCompetency

@Entity
@Table(name = "user_competency", schema = "public")
@JsonIdentityInfo(
          generator =ObjectIdGenerators.IntSequenceGenerator.class, 
          property = "id")
public class UserCompetency implements java.io.Serializable {
    private UserCompetencyId id;
    private Level level;
    private User user;
    private Competency competency;

    @EmbeddedId

    @AttributeOverrides({
            @AttributeOverride(name = "competencyId", column = @Column(name = "competency_id", nullable = false)),
            @AttributeOverride(name = "userId", column = @Column(name = "user_id", nullable = false)) })
    public UserCompetencyId getId() {
        return this.id;
    }

    public void setId(UserCompetencyId id) {
        this.id = id;
    }

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "level_id")
    public Level getLevel() {
        return this.level;
    }

    public void setLevel(Level level) {
        this.level = level;
    }

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "user_id", nullable = false, insertable = false, updatable = false)
    public User getUser() {
        return this.user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @ManyToOne(fetch = FetchType.EAGER,cascade=CascadeType.ALL)
    @JoinColumn(name = "competency_id", nullable = false, insertable = false, updatable = false)
    public Competency getCompetency() {
        return this.competency;
    }

    public void setCompetency(Competency competency) {
        this.competency = competency;
    }
}   

UserCompetencyId

@Embeddable
public class UserCompetencyId implements java.io.Serializable {

    private Long competencyId;
    private Long userId;

    public UserCompetencyId() {
    }

    public UserCompetencyId(Long competencyId, Long userId) {
        this.competencyId = competencyId;
        this.userId = userId;
    }


    @Column(name = "competency_id", nullable = false)
    public Long getCompetencyId() {
        return this.competencyId;
    }

    public void setCompetencyId(Long competencyId) {
        this.competencyId = competencyId;
    }

    @Column(name = "user_id", nullable = false)
    public Long getUserId() {
        return this.userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }

    public boolean equals(Object other) {
        if ((this == other))
            return true;
        if ((other == null))
            return false;
        if (!(other instanceof UserCompetencyId))
            return false;
        UserCompetencyId castOther = (UserCompetencyId) other;

        return (this.getCompetencyId() == castOther.getCompetencyId()) && (this.getUserId() == castOther.getUserId());
    }    
}

Supongamos que ya he registrado en las tablas de Usuario y Competencia y deseo asociar ambas cosas que estoy tratando de publicar de esta manera, pero me da un error del Método 405 no permitido.

se requiere ayuda, cuál debe ser la estructura de json que se publicará El usuario ya existirá y la competencia podría existir o se puede agregar y asociar nuevos con el usuario existente.