Backend Engineer, ID Platform

  • Tokyo
  • Remote OK - Anywhere in Japan
  • Full-time
  • October 11, 2022
Apply from Anywhere 👍
Relocation to Japan 👍
(Overseas visa sponsorship supported)
Language Requirements
Japanese: Not Required 👍
English: Business Level
Minimum Experience
Mid-level or above

Position Overview

Position Overview

  • Background

    • As Mercari continues to become a rising platform in the market attracting up to 100 million users, Merpay has laid out its mission to provide new value to customers on top of what Mercari already offers. 

    • The ID Platform team is a dedicated team who provide the authentication and authorization platform for both Mercari JP and Merpay.

    • As a software engineer in the ID Platform team, you will support Mercari Group’s growth with not only skills in the backend domain, but also expertise in authentication and authorization domain.

  • Working at Merpay

    • Merpay is home to some of the greatest experts within Mercari Group. Our commitment to a culture of openness allows members to discuss architecture on Slack channels organized by business domain, send pull requests to each other on GitHub, and share knowledge on the internal Wiki. We hold “Go Friday” and other weekly study groups for engineers but open to all, encouraging engineers to help one another grow. Some members have no experience developing in Go before they join, but we help turn them into Go enthusiasts early on through involvement in our internal Go community and “Gopher Dojo,” our short-term, intensive training. Members further develop their expertise while demonstrating their abilities at both internal and external engineering community events.

  • Job Description

    • Handle authentication and authorization platform development in Go

    • Providing authentication and authorization-related solutions to teams/projects across the whole Mercari group.

    • API/interface design for microservices using Protocol Buffers and gRPC

    • Improving services and measuring effectiveness using quantitative and qualitative analysis on user behavior logs, etc.

    • Design architecture and select middleware based on application requirements

    • Microservice performance tuning, monitoring, and alert handling

Bold Challenges

  • You will be able to work on a large-scale authentication and authorization platform that supports the huge customer base for both Mercari’s flea market and Merpay’s FinTech business. The platform is both internally and externally critical. It will not only support the internal microservices but also used by our partners for system integration purposes. 

  • This platform is built on our own. You will tackle difficult security and user experience problems along with your expertised team members.

  • You will dive into the deep ocean of OAuth 2, OpenID Connect, working with your team to renew the legacy authentication feature in a monolithic service by creating new microservices following the OpenID Connect standard.

  • During the process of designing and building the platform, you can gain a deep insight into related RFCs and Internet Drafts.

  • You will work in a super diverse team with teammates from more than 8 countries and areas to support other teams who use both Japanese and English.

Required Conditions

  • Shared belief in Merpay’s mission and values

  • Knowledge and experience in web application development

  • Enthusiasm in solving problems in authentication and authorization domain

  • Experience designing schemas and creating efficient queries for databases (such as RDB, NoSQL, etc.)

  • Experience operating web applications and conducting performance tuning, knowledge in security

  • Experience selecting middleware and designing software architecture

  • Ability to take ownership and lead the software development process

Preferred Experience

  • Experience in authentication and authorization development

  • Expertised knowledge in OAuth 2, OpenID Connect and other well-known auth schemes.

  • Experience developing and operating using Go, PHP, GCP

  • Experience developing and operating large-scale, high traffic system

  • Experience establishing new services and tackling the challenges in the growth phase of a service

  • Experience as developer lead or management / experience improving the development process

  • Experience in statistical data analysis

Screening Criteria

  • Desire to use technology to push the finance industry forward

  • Ability to collaborate with members from diverse backgrounds to take on goals

  • Ability to continuously grow alongside teammates, without becoming complacent or satisfied with the status quo

  • Ability to resolve the organization’s challenges through excellent communication skills

  • Strong willingness to solve problems in authentication and authorization domain.

  • We want to get a thorough understanding of your experience and skills by asking interview questions about specific situations, tasks, actions, and results (STAR)

  *Check here for more details

Technical Assessment Criteria

  • You will be working on a small backend project for 1 week.

  • It may take you around 8 hours to finish, though it depends on your experience.

  • You can choose Go or Java assessment.

  • Through your technical assessment, we would like to see if you are the engineer we want to work together with, including but not limited to the following points:

    • If your code is production ready.

    • If your codebase is easy for others to commit or take over.

    • If you or others can easily find the improvement points and work on them.

Language Requirements

  • English: Independent (CEFR - B2)

  • Japanese: Basic (CEFR - A2) optional

Working Conditions

Employment Status


  • Probationary period: First 3 months after joining the company. (During this period your contract conditions will be the same as that of a permanent employee.)



  • Smoking is prohibited within our offices

  • Mercari has introduced a work style policy called “Your Choice.” Each member is free to choose whether they want to work in the office or work fully remote. *Exceptions made for certain kinds of work.

Merpay was established in 2017 as a group company of Mercari. They're developing financial services with a focus on payment and credit businesses.

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Backend Engineer, ID Platform at Merpay