Spring-boot 2 ignoring Hikari specific properties - spring-boot

Question

I'm trying to configure some Hikari specific properties for the datasource, and can't figure out how to do that left alone, that I don't even see how it suppose to work.
According to the Spring-boot doc you should be able to configure lots of additional props, for example, spring.datasource.hikari.transaction-isolation. So I have application.properties file with a content
spring.application.name=My App
# DB
spring.datasource.url=jdbc:sqlserver://localhost;databaseName=dbname
spring.datasource.username=user
spring.datasource.password=passw
spring.datasource.driverClassName=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.hikari.minimumIdle=5
spring.datasource.hikari.maximumPoolSize=30
spring.datasource.hikari.transaction-isolation=TRANSACTION_READ_COMMITTED
From what I understand from the docs, this should be enough for Spring-boot 2 to initialize Hickory datasource with the additional properties. However, when I run my application I can see that the datasource created with only generic spring.datasource.* properties.
I debugged application initialisation and looked at org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration class. I can see Spring uses Hikari datasource and creates an instance of HikariDataSource.class, but created datasource doesn't have any specific properties set. What I don't understand, is how it even possible to have some additional properties if the properties parameter has the actual type of DataSourceProperties which has no knowledge of any hikari specific properties. I thought it would be something hikari specific but it is not.
/**
* Hikari DataSource configuration.
*/
#Configuration(proxyBeanMethods = false)
#ConditionalOnClass(HikariDataSource.class)
#ConditionalOnMissingBean(DataSource.class)
#ConditionalOnProperty(name = "spring.datasource.type", havingValue = "com.zaxxer.hikari.HikariDataSource",
matchIfMissing = true)
static class Hikari {
#Bean
#ConfigurationProperties(prefix = "spring.datasource.hikari")
HikariDataSource dataSource(DataSourceProperties properties) {
HikariDataSource dataSource = createDataSource(properties, HikariDataSource.class);
if (StringUtils.hasText(properties.getName())) {
dataSource.setPoolName(properties.getName());
}
return dataSource;
}
}
I can imagine that there maybe another call to configure the datasource later, but I can't find it and when inspecting datasource, at runtime, I can see they not set. I must be missing something here, so any help would be appreciated.
P.S. I also tried to use manual configuration but hit an another issue with Flyway.