Dear Akarsh,
' Deputation' in employment is basically a process of hiring out or exchange of the services of an employee for a specified period between two employers by means of an agreement with the consent of the employee concerned. This signifies the presence of two employers and one employee viz., the original employer, the foreign employer and the deputationist. Here the contract of employment between the original employer and the employee continues despite the deputation for the basic features of employment such as disciplinary control, sanction of increments, leave sanction, promotion, recall etc. Thus the original employer remains the de jure employer while the foreign employer being the de facto employer in so far as the day to day performance of the deputationist is concerned. And the employee on deputation retains his right to employment which is called as ' lien' with the original employer so long as the deputation continues.
If you consider this legal position dispassionately while you intend to exit during the phase of your deputation, I do hope that you will accept that your resignation should be routed to the original employer through the foreign employer and accepted by the former and the relief arrangements to be made by both.
It is for the original employer to issue the experience certificate.