SpringBoot MongoDB authentication fails without uri attribute in config after upgrading from 3.0.7 to 3.1.0

After upgrading from Spring Boot 3.0.7 to Spring Boot 3.1.0, my project failed to authenticate with the MongoDB database.

I'm using the spring-boot-starter-data-mongodb dependency.

This is part of my application.yml config related to MongoDB:

spring:
  data:
    mongodb:
      database: academyDB
      host: 127.0.0.1
      port: 27017
      username: user
      password: password
      authentication-database: admin
      auto-index-creation: true

The error I'm getting:

Caused by: com.mongodb.MongoCommandException: Command failed with error 18 (AuthenticationFailed): 'Authentication failed.' on server 127.0.0.1:27017. The full response is {"ok": 0.0, "errmsg": "Authentication failed.", "code": 18, "codeName": "AuthenticationFailed"}
    at com.mongodb.internal.connection.ProtocolHelper.getCommandFailureException(ProtocolHelper.java:205)
    at com.mongodb.internal.connection.InternalStreamConnection.receiveCommandMessageResponse(InternalStreamConnection.java:443)
...

I just figured out, that if I'm using the uri attribute in my application.yml, the application starts successful and the MongoDB connection is set up as well:

spring:
    data:
      mongodb:
        uri: mongodb://root:mongo@localhost:27017/${spring.data.mongodb.database}?authSource=${spring.data.mongodb.authentication-database}&readPreference=primaryPreferred&directConnection=true
        database: academyDB
        authentication-database: admin

If there are any changes in the way spring uses the configuration to authenticate against MongoDB, they are missing in the release notes and in the documentation. So probably it's a bug.

The alternative was to use the discrete properties is still specified in the documentation

I hope someone can clarify this issue. Thanks!

Comment From: scottfrederick

Duplicates #35567