BBVA has recruited Simple co-founder Shamir Karkal to build a platform that would open the bank's application program interfaces to outside fintech companies.

Karkal has been named head of open APIs, he announced Tuesday in a blog post on the bank's website. Additionally, the blog post disclosed that the Madrid-based banking company is conducting early testing on an open API platform with a few partners in Spain.

The rehiring comes at a time when banks and fintech companies are looking at ways to partner. Open APIs facilitate such collaboration by giving outside software developers easier (though controlled) access to a bank's data.

Karkal stepped down from Simple, where he was also chief financial officer, in June 2015, about 15 months after the digital-only "neobank" was acquired by BBVA. In the blog post, Karkal said that acquisition familiarized him with the bank, whose U.S. operations are based in Birmingham, Ala.

He has rejoined BBVA in the newly created position to mimic in banking what Amazon created with its Web services division.

"When Amazon Web Services launched in 2006, people wondered why an online retailer was launching a new business offering companies server capacity from its own technology platform. I think that question has been answered fairly robustly: In the quarter ending in December 2015, AWS had revenues of $2.4 billion and operating income of $687 million," Karkal wrote.

"Amazon has built the world's fastest-growing technology business (yes, faster than Google and Apple) by letting third parties build businesses using its technology platform," he added.

BBVA is among the earlier adopters of open APIs. For instance, its BBVA Compass Bank unit provides a startup called Dwolla with access to its APIs for real-time money transfers.

Although the opportunity to build an open platform holds great promise, the company must build it methodically with security and privacy of customer data as the highest priorities, Karkal said.

"Of course building an open API platform for banking is a huge challenge as well," he said.