One SQL Server credential to each report pbix

Hello everyone. 

I need to understand something:

- I create a Report1.pbix;

- So, I do: File >> Options and settings >> Data source options settings

- The option "Data sources in current file" is checked;

- I do double click in my datasource

- In credentials, I click "Edit", choose "Database", put my database user and password (eg: john/doe)

- OK. Everything works fine! I can reach my tables!

- I create a Report2.pbix;

- So, I do: File >> Options and settings >> Data source options settings

- The option "Data sources in current file" is checked;

- I do double click in my datasource

- In credentials, I click "Edit", choose "Database", put my database user and password (eg: mary/lou)

- OK. Everything works fine! I can reach my tables!

IF I reopen my Report1.pbix, it shows a credentials error message. When I open the Data source options again, the user and password is "mary/lou" (the last I did).

If I change to the correct (john/doe), the Report2.pbix shows the credentials error, because it is trying to use john/doe

Why the connections string is not saved by *.pbix file?

It is saved in somewhere in my computer or something like that?

I need Report1.pbix with a credentials that is different of the Report2.pbix.