Explain the OAuth2 authorization code flow at a high level for a web app.
PICTURE THIS: A SENTENCE BECOMES TOKENS
The model does not read letters like humans. It reads these pieces, then predicts the next one.
Simple meaning
The user is redirected to the identity provider, logs in, and the browser comes back with a short-lived code.
WHY — Auth instead of guessing?
Why interviewers care about Auth:
who only read docs from people who shipped.
and tied to Backend work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens with tokens?
Before the model can read a sentence, it goes through these steps:
- 1The user is redirected
to the identity provider, logs in, and the browser comes back with a short-lived code.
- 2The backend exchanges that
code plus a client secret for tokens, so the secret never sits in JavaScript.
- 3PKCE is added for
public clients like mobile apps that cannot hold a secret.
- 4Context mix
Attention looks at nearby tokens together.
- 5Next token
The model scores what should come next.
- 6Decode
IDs turn back into readable text.
EXAMPLE — See it in action
Let's see how a real sentence is tokenized (tokens may vary by model):
Note: Actual tokens and IDs depend on the tokenizer (e.g., GPT, Llama, etc.).
Key takeaway
The user is redirected to the identity provider, logs in, and the browser comes back with a short-lived code. The backend exchanges that code plus a client secret for tokens, so the secret never sits in JavaScript.