Default Spring Data MongoDB properties values - spring-boot

Question

I have a new MongoDB, that means there's no user, password and/or an authentication database.
Translating this to a .properties file, this should be:
spring.data.mongodb.host=localhost
spring.data.mongodb.port=27017
...and for .yaml/.yml:
spring:
data:
mongodb:
host: localhost
port: 27017
Now let's suppose I want to use environment variables instead, if they're set, like this:
spring:
data:
mongodb:
host: ${MONGODB_HOST:localhost}
port: ${MONGODB_PORT:27017}
Everything until now works as expected.
What I want to achieve is the same for the spring.data.mongodb.user, spring.data.mongodb.password and spring.data.mongodb.authentication-database properties. I've tried doing the same technique for these properties, but in case they're not found in the environment, an exception is thrown, like this:
spring:
data:
mongodb:
host: ${MONGODB_HOST:localhost}
port: ${MONGODB_PORT:27017}
username: ${MONGODB_USERNAME}
password: ${MONGODB_PASSWORD}
authentication-database: ${MONGODB_AUTHENTICATION_DATABASE}
I have even tried setting empty/blank valuesm like ${MONGODB_USERNAME:}, ${MONGODB_USERNAME:''} and ${MONGODB_USERNAME:""}.
How do I get to achieve this? Is it even possible?

Answer 1

I've not tried this, but Spring boot should be able to pickup environment variables and use them as properties without having to put them in the yaml file. For example if you name a OS environment variable SPRING_DATA_MONGODB_USERNAME the value should show up in the spring property spring.data.mongodb.username. This would allow you to specify the username property only when you require it.
The other way to do this is to use externalised config. If you are booting your application from a fat jar, an application.yml outside the jar in the same directory can add in your additional properties:
spring:
data:
mongodb:
username: fred
password: password
without affecting the properties specified in the application.yml provided inside the jar.
There's a long ordered list of where spring-boot looks for properties documented here.