We are pleased to announce that freee K.K. (freee) has adopted Authlete to modernize its OAuth 2.0 infrastructure for the freee API, its public API.
Under its mission “Empower Small Businesses to Take Center Stage,” freee develops and provides SaaS-based cloud services, including its integrated cloud accounting software, freee Accounting, which streamlines accounting, human resources, and labor management.
In addition, freee offers the freee API as an open platform that enables the integration of freee’s features with third-party services, business partners, and financial institutions. freee also operates the freee App Store for third-party developers, building an ecosystem that strengthens integration with external service apps.
freee has been working on open APIs since 2015 and adopted OAuth 2.0, an open standard for API access authorization, at an early stage, implementing and operating its own OAuth 2.0 infrastructure in-house. However, nearly 10 years after launching the OAuth 2.0 infrastructure, the rapid growth of the platform and app store led to increased maintenance costs for the authorization infrastructure, and scalability became an issue. Furthermore, it became difficult to continually keep up with the latest OAuth 2.0 extensions and best practices.
Therefore, freee decided to upgrade its authorization infrastructure and transform it into a platform that implements advanced API security capable of supporting the sustainable growth of its business and ecosystem.
When building the new infrastructure, freee needed to maintain the existing API authorization specifications as much as possible to minimize the impact on customers and partners using the freee API. The company considered both building the infrastructure entirely in-house and introducing an external service.
“Because freee’s ID management, which is driven by our specific domain logic, and authentication infrastructure had been built internally as independent systems, an all-in-one IDaaS solution that included ID management was unable to meet our requirements,” said Daiki Murayama, Engineering Manager at freee.
“Therefore, we initially considered rebuilding the system completely in-house, but determined that it wouldn’t be easy to implement the OAuth 2.0 functionality from scratch in a way that would withstand feature expansions in the future. We therefore began looking into an operational method that would meet the unique domain requirements of B2B SaaS without relying on scarce engineering talent with deep OAuth expertise,” said Murayama.
Ultimately, freee chose Authlete as it is highly customizable and met their cost requirements. Murayama explained the benefits of adopting Authlete as follows:
“Authlete provided the comprehensive features necessary to migrate from the old OAuth 2.0 infrastructure to the new one with zero downtime. It also allowed us to offload the complex aspects of in-house development to the Authlete API, enabling us to control everything from the authorization server endpoint URL to the login screen and even the detailed interface parameters. Furthermore, in addition to maintaining the existing specifications, we can now also accommodate changes and evolution of the OAuth 2.0 specifications.”
Murayama also said that Authlete’s unique features and architecture contributed to the smooth construction of the new infrastructure.
“As Authlete provides a wide variety of configuration options for OAuth 2.0, we were able to incorporate our existing API authorization specifications into the new infrastructure as is. Also, because Authlete’s architecture does not store user information, we were able to utilize our existing data structures for users and business entities specific to our B2B SaaS service without modification,” said Murayama.
freee’s new infrastructure, built using Authlete, was released in July 2025 and has been running stably ever since. According to Murayama, the new infrastructure “has led to increased agility for their team.”
Read more customer success stories here.
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