Authentication
intermediateOAuth 2.0 Explained
OAuth 2.0 is an authorization framework that lets one application access resources on a user's behalf without ever seeing that user's password.
Concepts
Short, practical explanations of software engineering concepts — written to be understood once, not memorised twice.
Showing 15 of 15 concepts
Authentication3
Authentication
beginnerWhat is a JWT?
A JWT is a signed, self-contained token format that lets a server verify claims about a user without a database lookup, at the cost of being hard to revoke early.
Authentication
beginnerWhat is PKCE?
PKCE hardens the OAuth 2.0 authorization code flow against interception attacks by binding the authorization request to the token exchange with a one-time secret.
Networking2
Networking
beginnerNAT and Port Forwarding: Public Port vs. Listening Port
A packet can arrive at one port number and be delivered to another. Once you know where that rewrite happens, firewall rules stop being guesswork — you allow the port the service actually receives traffic on inside the machine, not the port you typed into the client.
Networking
intermediateHTTP/1.1 vs HTTP/2 vs HTTP/3
Each HTTP version fixes a specific bottleneck in the one before it, moving from one request per connection to multiplexed streams to a transport that no longer blocks on packet loss.
Databases2
Databases
intermediateWhat is Write-Ahead Logging (WAL)?
Write-Ahead Logging (WAL) is a technique used in databases to ensure data integrity and durability by recording changes to a log before applying them to the database.
Databases
beginnerWhat is a Database Index?
A database index trades extra storage and slower writes for the ability to find rows without scanning the whole table, the same trade a book's index makes for its reader.
Caching1
Caching
intermediateWhat is a Cache Stampede?
A cache stampede happens when a popular cached value expires and every waiting request rushes the origin at once, turning a cache miss into a self-inflicted denial of service.
Distributed Systems3
Distributed Systems
advancedWhat is Consistent Hashing?
Consistent hashing distributes keys across nodes so that adding or removing a node only reshuffles a small fraction of keys, instead of nearly all of them.
Distributed Systems
intermediateWhat is Idempotency?
An idempotent operation produces the same result no matter how many times it's applied, which is the property that makes retrying a failed request safe in a distributed system.
Distributed Systems
advancedWhat is the Outbox Pattern?
The outbox pattern makes writing to a database and publishing an event look atomic by writing both in one transaction and relaying the event asynchronously.
Architecture1
Architecture
beginnerWhat is a Circuit Breaker?
A circuit breaker stops a service from repeatedly calling a dependency that's already failing, giving it room to recover instead of being buried under retries.
Security2
Security
beginnerchmod, chown and What 600 Actually Means
Every file on a Unix system carries an owner, a group and nine permission bits. This is what those bits mean, why 600 and 700 keep showing up, how the octal digits are built, and the rules that make permissions behave differently than most people assume.
Security
beginnerWhat is an SSH Key?
An SSH key is a public/private keypair that proves who you are to a server without ever sending a secret over the wire — replacing passwords with a challenge you can only answer if you hold the private half.
Scalability1
Scalability
intermediateRate Limiting Algorithms: Which One to Pick and Why
Token bucket, leaky bucket, fixed window, sliding window log and sliding window counter — how each one decides, where each one breaks, and how to choose between them.
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