こちらを参考にしています。
https://qiita.com/KoheiKanagu/items/2ba5f49632d9868159fc#group

◆SpringMongoConfiguration.java

package com.yaskawa.DB.config;

import java.util.ArrayList;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.data.mongodb.config.AbstractMongoConfiguration;
import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
import com.mongodb.Mongo;
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
import com.mongodb.ServerAddress;

public class SpringMongoConfiguration extends AbstractMongoConfiguration {

    @Value("${spring.data.mongodb.host}")
    private String mongoHost;

    @Value("${spring.data.mongodb.port}")
    private int mongoPort;

    @Value("${spring.data.mongodb.database}")
    private String mongoDB;

    @Value("${spring.data.mongodb.username}")
    private String username;
    @Value("${spring.data.mongodb.password}")
    private String password;

    @Override
    public MongoMappingContext mongoMappingContext() throws ClassNotFoundException {
        // TODO 自動生成されたメソッド・スタブ
        return super.mongoMappingContext();
    }


    @Override
    @Bean
    public Mongo mongo() throws Exception {
        System.out.println("mongo host: " + mongoHost);
        System.out.println("mongo db: " + mongoDB);

        MongoCredential credential =
                MongoCredential.createMongoCRCredential(username, mongoDB, password.toCharArray());
        ServerAddress serverAddress = new ServerAddress(mongoHost, mongoPort);


        return new MongoClient(serverAddress, new ArrayList<MongoCredential>() {
            /**
             * 
             */
            private static final long serialVersionUID = 2121507982881939791L;

            {
                add(credential);
            }
        });
    }


    @Override
    protected String getDatabaseName() {
        // TODO 自動生成されたメソッド・スタブ
        return mongoDB;
    }

}

◆pom.xml

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.9.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <java.version>1.8</java.version>
</properties>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-mongodb</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-tomcat</artifactId>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>
<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

◆application.properties

spring.data.mongodb.username: user
spring.data.mongodb.password: password
spring.data.mongodb.host: localhost
spring.data.mongodb.port: 27017
spring.data.mongodb.database: test
spring.data.mongodb.uri=mongodb://user:password@localhost/test★

★がないと以下のエラーが発生していました

com.mongodb.MongoSecurityException: Exception authenticating MongoCredential{mechanism=null, userName='ycpuser', source='YPL', password=<hidden>, mechanismProperties={}}

上記の状態でSpringbootアプリケーションの実行を行うと以下のようなエラーが出てしまいます。
何か設定で足りない部分などありますでしょうか?

Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2018-01-16 17:44:48.183 ERROR 5748 --- [           main] o.s.boot.SpringApplication               : Application startup failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mongo' defined in class path resource [org/springframework/boot/autoconfigure/mongo/MongoAutoConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.mongodb.MongoClient]: Factory method 'mongo' threw exception; nested exception is java.lang.IllegalStateException: Invalid mongo configuration, either uri or host/port/credentials must be specified
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:599) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1173) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1067) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at com.test.TestApplication.main(YplWebApplication.java:10) [classes/:na]
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.mongodb.MongoClient]: Factory method 'mongo' threw exception; nested exception is java.lang.IllegalStateException: Invalid mongo configuration, either uri or host/port/credentials must be specified
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:189) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    ... 18 common frames omitted
Caused by: java.lang.IllegalStateException: Invalid mongo configuration, either uri or host/port/credentials must be specified
    at org.springframework.boot.autoconfigure.mongo.MongoProperties.createNetworkMongoClient(MongoProperties.java:237) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.autoconfigure.mongo.MongoProperties.createMongoClient(MongoProperties.java:208) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration.mongo(MongoAutoConfiguration.java:73) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration$$EnhancerBySpringCGLIB$$74f1bfef.CGLIB$mongo$1(<generated>) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration$$EnhancerBySpringCGLIB$$74f1bfef$$FastClassBySpringCGLIB$$fa24578d.invoke(<generated>) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228) ~[spring-core-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:358) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration$$EnhancerBySpringCGLIB$$74f1bfef.mongo(<generated>) ~[spring-boot-autoconfigure-1.5.9.RELEASE.jar:1.5.9.RELEASE]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_92]
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_92]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_92]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_92]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:162) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    ... 19 common frames omitted