JdbcOneTimeTokenService.setCleanupCron

Spring Security uses setter methods for optional member variables. Allows
for a null cleanupCron to disable the cleanup.

In a clustered environment it is likely that users do not want all nodes
to be performing a cleanup because it will cause contention on the ott
table.

Another example is if a user wants to invoke cleanUpExpiredTokens with a
different strategy all together, they might want to disable the cron job.

Issue gh-15735

core/src/test/java/org/springframework/security/authentication/ott/JdbcOneTimeTokenServiceTests.java

@@ -175,6 +175,17 @@ public class JdbcOneTimeTokenServiceTests {
 		assertThat(deletedOneTimeToken2).isNull();
 	}
 
+	@Test
+	void setCleanupChronWhenNullThenNoException() {
+		this.oneTimeTokenService.setCleanupCron(null);
+	}
+
+	@Test
+	void setCleanupChronWhenAlreadyNullThenNoException() {
+		this.oneTimeTokenService.setCleanupCron(null);
+		this.oneTimeTokenService.setCleanupCron(null);
+	}
+
 	private void saveToken(OneTimeToken oneTimeToken) {
 		List<SqlParameterValue> parameters = this.oneTimeTokenParametersMapper.apply(oneTimeToken);
 		PreparedStatementSetter pss = new ArgumentPreparedStatementSetter(parameters.toArray());