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Your sentence is an example of "legalese," and frankly, it is not worded very well!
The one doing the granting is an unspecified person, institution, or "entity." Normally, the guarantor of the loan can be the borrower or someone else (as when an individual has someone co-sign for the loan, and this person is on the hook for paying back the loan if the borrower defaults).
The person or institution (e.g., a bank) making the loan is the one doing the granting. This fact is implied in the sentence as you've copied it. The word may also implies there are certain criteria which must be met in order for this "entity" to vouch for the borrower.
Who or what this third party might be--well, I haven't a clue, though a lawyer might.