Quick post mostly for my own reference since I always need to re-learn how to do this. This used to be more difficult in older versions of Spark, but on 2.4/3.0, all you have to do is:

wget https://repo1.maven.org/maven2/com/amazonaws/aws-java-sdk/1.7.4/aws-java-sdk-1.7.4.jar -P $SPARK_HOME/jars/
wget https://repo1.maven.org/maven2/org/apache/hadoop/hadoop-aws/2.7.3/hadoop-aws-2.7.3.jar -P $SPARK_HOME/jars/