You have to verify your credentials in MAVEN_HOME/conf/settings.xml section servers
<server>
<id>nexus</id>
<username>deploy</username>
<password>123456</password>
</server>
Id must match with id in distribution management in your pom.xml
<distributionManagement>
<repository>
<id>nexus</id>
<url>...</url>
</repository>
</distributionManagement>