Check if value from one dataframe exists in another dataframe and create column

I am looking to compare values of columns in two different datasets and create a column with the results that have matched.

DF1:

 Dates
0   2021-10-01
1   2021-10-02
2   2021-10-03
3   2021-10-04
4   2021-10-05
5   2021-10-06
6   2021-10-07

DF2 =

StartDate    User
2021-10-04   Doe, John
2021-10-07   Ann, Mary
2021-10-07   Doe, John

Expected Result

DF1:

 Dates            User
0   2021-10-01
1   2021-10-02
2   2021-10-03
3   2021-10-04    Doe, John
4   2021-10-05
5   2021-10-06
6   2021-10-07    Ann, Mary; Doe, John

I can see the matches using the following code:

df1= df2.loc[df2['StartDate'].isin(df1['Dates']), 'User']

And i can return a 1/0 with the following:

df1= df1.assign(result=df1['Dates'].isin(df2['StartDate']).astype(int))

However, i cannot seem to merge them both

Answer

df.join(df2.groupby('StartDate')['User'].apply('; '.join), how='left', on='Dates').fillna('')

Output:

>>> df
       Dates          User
0 2021-10-01              
1 2021-10-02              
2 2021-10-03              
3 2021-10-04         Test1
4 2021-10-05              
5 2021-10-06              
6 2021-10-07  Test2, Test1