How Do I match two Data Frames in Pandas with multiple matches?

Question

I have 2 data frames I want to match some data from one data frame and append it on another.

df1 looks like this:

sourceId	firstName	lastName
1234	John	Doe
5678	Sally	Green
9101	Chlodovech	Anderson

df2 looks like this:

sourceId	agentId
123456789	1234,5678
987654321	9101
143216546	1234,5678

I want my Final Data Frame to look like this:

sourceId	firstName	lastName	agentId
1234	John	Doe	123456789,143216546
5678	Sally	Green	123456789,143216546
9101	Chlodovech	Anderson	987654321

Usually appending stuff is easy but I'm not quite sure how to match this data up, and then append the matches with commas in-between them. I'm fairly new to using pandas so any help is appreciated.