Hi,
Thanks for reaching out.
Just to confirm my understanding, you wish to let users login to your application using your OAuth2 Credentials. Then, user inputs their clientCustomerId for the application to link the account to your MCC. If my unedrstanding is correct, you can link accounts using the
CustomerClientLinkService.MutateCustomerClientLink in your MCC account. You may refer to this
guide for more details on how to do so.
For steps 1 and 2, you have to implement this on your end.
If I misunderstood your objective, kindly elaborate further so I can better assist you.
Regards,
Dannison
Google Ads API Team

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