It is my understanding you need to add spring source repository for milestones to your project pom:
Code:
<repository>
<snapshots>
<enabled>false</enabled>
</snapshots>
<id>org.springframework.maven.milestone</id>
<name>Spring Maven Milestone Repository</name>
<url>http://maven.springframework.org/milestone</url>
</repository>
Then you need to add the dependencies for Milestone 3, which was the latest milestone last time I checked:
Code:
<dependency>
<groupId>org.springframework.security.oauth</groupId>
<artifactId>spring-security-oauth</artifactId>
<version>1.0.0.M3</version>
<scope>compile</scope>
</dependency>
As far as I know, the reason its not in central maven repository it's because not finalized official version.