core/src/main/java/org/springframework/security/core/authority/AuthorityUtils.java
public static Set<String> authorityListToSet(
			Collection<? extends GrantedAuthority> userAuthorities) {
		Assert.notNull(userAuthorities, "userAuthorities cannot be null");
		Set<String> set = new HashSet<>(userAuthorities.size());

		for (GrantedAuthority authority : userAuthorities) {
			set.add(authority.getAuthority());
		}

		return set;
	}
public static Set<String> authorityListToSet(
			Collection<? extends GrantedAuthority> userAuthorities) {
		Assert.notNull(userAuthorities, "userAuthorities cannot be null");
		Set<String> set = new HashSet<>(userAuthorities.size());

		for (GrantedAuthority authority : userAuthorities) {
			set.add(authority.getAuthority());
		}

		return set;
	}
Converts an array of GrantedAuthority objects to a Set.
@return a Set of the Strings obtained from each call to
GrantedAuthority.getAuthority()