Senior Java Engineer — Digital Signatures, Access Control, Integrations

I build Java backends that have to survive an audit — and I fix the ones that didn't. Spring Boot, PostgreSQL, Kafka, Kubernetes, plus what most backend developers avoid: certificates, digital signatures, and access control that actually holds.

• Apache Kafka
• Docker
• Hibernate (Java)
• Java (allg.)6 J.
• Kryptographie
• Kubernetes
• Postgresql
• Spring Boot
• Spring Framework2 J.
• SQL

Java engineer with ten years of backend experience — banking, billing and corporate systems. I work on the part of the stack where a mistake costs more than a delayed release.

WHAT I DO

Digital signatures and cryptography. CAdES signing and format conversion, certificate validation chains, revocation checking via OCSP with CRL fallback, trust-list loading and refresh, mTLS between services. If your signatures fail validation in production and nobody can tell you why, that is my day job.

Authentication and authorization. JWT issuing and validation on Spring Security, OAuth 2.0, Keycloak and OIDC for service-to-service access.

Access control that cannot be bypassed. RBAC and ACL filtering compiled into the SQL query rather than applied after the result set, including pagination and counters that stay correct — so a user cannot read, or even count, a row they are not entitled to.

Microservices. Java 21 and Spring Boot 3 on PostgreSQL, Kafka, Redis and Kubernetes. Multi-module Maven builds, Liquibase and Flyway migrations with working rollbacks, GitLab CI, Prometheus metrics.

Integrations with external and government APIs. Rate limiting inside the client, retries with backoff, idempotency so a repeat does not create a duplicate document, bounded timeouts.

Reports and printable forms. PDF, XLSX and HTML generated from a single template, so changing a form is a template edit rather than a release.

HOW I WORK

I read the code before I propose anything. I tell you when a request is a bad idea, and why. Estimates are fixed and given after I have read the code. Source code stays with you.

Tests are written for the failure path, not only the happy one: Testcontainers with a real database, WireMock for external APIs, Toxiproxy for broken connections.

Working remotely from Moscow. English and Russian; German at a basic level.

Languages & frameworks: Java 8-21, Spring Boot, Spring Framework, Spring Security, Spring Data, Hibernate/JPA, jOOQ, JDBC, HikariCP

Databases & caching: PostgreSQL, Oracle, MySQL, Firebird, PL/SQL, Redis, Apache Ignite

Messaging & integration: Apache Kafka, ActiveMQ/Artemis, RabbitMQ, REST, OpenAPI/Swagger, SOAP, Mule ESB, Camunda/BPMN, MinIO/S3

Security & cryptography: CAdES, OCSP, CRL, TSL, mTLS, X.509, PKI, Bouncy Castle, JWT, OAuth 2.0, OIDC, Keycloak, RBAC, ACL

Documents & reporting: JasperReports, Apache POI, Apache Lucene

Infrastructure & delivery: Docker, Kubernetes, Helm, nginx, GitLab CI, Maven, Gradle, Liquibase, Flyway, Prometheus, Spring Actuator

Testing & profiling: JUnit 4/5, Mockito, Testcontainers, WireMock, Toxiproxy, JMeter, Java Flight Recorder, VisualVM

Tools & systems: Git, IntelliJ IDEA, Linux, FreeBSD