Deepak Prasad

POST access tokens to Keycloak token introspection with curl and a confidential client, read active true or false after expiry logout and audience mismatch, and compare local JWT verification on Keycloak 26.7.3.

Walk through Keycloak Device Authorization Grant on a public CLI client: request device and user codes, poll with interval and slow_down, complete browser verification, and call UserInfo after approval.

Request Keycloak offline tokens with offline_access through Authorization Code flow, refresh after SSO logout, tune Offline Session Idle and Max Limited, rotate and revoke safely, and compare offline refresh tokens with …

Request a Keycloak client_credentials access token with curl and HTTP Basic auth, decode service-account claims (sub, azp, aud, roles), check audience and roles at orders-api, and tell token-endpoint 401 apart from API …

Use Keycloak refresh tokens with curl, enable Revoke Refresh Token and Max Reuse, relate refresh_expires_in to client and SSO sessions, and diagnose invalid_grant after logout, idle timeout, or token reuse on Keycloak …

Configure Keycloak PKCE on a public client with S256, generate a code verifier and challenge, complete Authorization Code flow, and prove a stolen code fails without the verifier on Keycloak 26.7.3.

Walk through Keycloak Standard Flow with a confidential server-side client: build the authorization URL, exchange the code with curl, validate state and nonce, refresh tokens, and reproduce common invalid_grant errors.

Learn how Keycloak user sessions, client sessions and offline sessions work, how they relate to tokens and SSO, and how to view or revoke them.

Configure a public Keycloak OIDC client with PKCE, run Authorization Code flow, inspect ID and access JWTs, call UserInfo, and validate the bearer token at a small Python API on Keycloak 26.7.3.

Understand sshd ssh-rsa algorithm is disabled on RHEL 9 and 10, when RSA-SHA2 logins still work, and when to upgrade clients or allow a scoped ssh-rsa exception.

Fix SSH "Bad server host key: Invalid key length" caused by 1024-bit RSA host keys, RequiredRSASize, RHEL crypto policies, or stale known_hosts entries.

Free CKS exam prep course covering all six Linux Foundation security domains, with hands-on kubeadm labs for kube-bench, Trivy, Cosign, Falco, and gVisor.

Free CKA exam prep course covering all five Linux Foundation domains, with hands-on kubeadm labs on Rocky Linux VMs tested on Kubernetes 1.36.

Free CKAD exam prep course covering all five Linux Foundation domains, with hands-on labs, 25 practice tasks, and a cheat sheet tested on Kubernetes 1.36.

Free Kubernetes Operator course on CRDs, controller-runtime, and Go, Helm, and hybrid operators, with hands-on labs tested on Operator SDK 1.42 and kind.

Free Kubernetes tutorial from first cluster to Helm, RBAC, and upgrades, with hands-on lessons run on Kubernetes 1.36 kubeadm clusters, local and on AWS.

Free Golang tutorial for beginners: 200+ runnable lessons on modules, structs, errors, goroutines, HTTP and gRPC APIs, databases, testing, and Docker.

Free Java tutorial for beginners: 100+ lessons on OOP, collections, lambdas, file I/O, exceptions, and multithreading, with examples run on OpenJDK 17.

Free JavaScript tutorial for beginners: 120+ runnable lessons on ES6+ syntax, arrays, objects, classes, async/await, the DOM, and common error fixes.

Free Node.js tutorial for beginners: 60 hands-on lessons on files, async code, HTTPS servers, Express, MongoDB, MySQL, Passport login, and deployment.

Free Python tutorial for beginners: 160+ hands-on lessons on data types, loops, OOP, file I/O, regex, concurrency, and Flask, tested on Python 3.13.

Free Podman tutorial tested on RHEL 10.2 with Podman 5.8: run rootless containers, build images, set up networking, and deploy services with Quadlet.

Free Git and GitHub tutorial with hands-on examples tested on Git 2.52: commits, branches, merge and rebase, remotes, undo, and history cleanup.

Free hands-on Microsoft Azure tutorial for beginners: Entra ID, VMs, App Service, AKS, Blob Storage, VPN, Front Door, ARM templates, and cost control.

Free Ansible tutorial and Red Hat RHCE EX294 exam prep with hands-on labs on Rocky Linux 10: playbooks, roles, Vault, and RHCSA tasks automated end to end.

Free Keycloak tutorial and IAM course covering realms, clients, OIDC, LDAP federation, SAML, and operations, with Podman labs tested on Keycloak 26.7.

Free 389 Directory Server course: dscreate, dsconf and dsidm, TLS, ACIs, password policy, replication, and LMDB tuning, tested on 389-ds-base 3.2.

Free keytool tutorial for Java keystores and truststores: PKCS12, CSRs, chain imports, cacerts, PKIX fixes, and Spring Boot and Tomcat HTTPS on JDK 21.

Free OpenLDAP tutorial for Linux admins: cn=config and MDB, TLS, ACLs, password policy, SSSD clients, replication, and backup, tested on OpenLDAP 2.6.

Free OpenSSL and PKI tutorial: generate keys and CSRs, build a root and intermediate CA, issue SAN certificates, set up mTLS, then renew and revoke.