Decode a JWT string without libraries
Company: Microsoft
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: hard
Interview Round: Onsite
Implement a function that **decodes** (but does not necessarily verify) a JWT token.
A JWT is a string of the form:
```
<base64url(header)>.<base64url(payload)>.<base64url(signature)>
```
Where `header` and `payload` are UTF-8 JSON.
### Task
Write a function (language: **C#**) that:
1. Splits the token into 3 parts.
2. Performs **Base64URL** decoding (note: `-` and `_` instead of `+` and `/`, and padding `=` may be missing).
3. Decodes the header and payload into JSON strings (or into dictionaries/objects if you prefer).
4. Returns the decoded header and payload.
### Notes / Edge cases
- Handle missing padding correctly.
- If the token is malformed (wrong number of segments, invalid base64, non-JSON payload), return an error / throw.
- You do **not** need to validate the signature unless explicitly stated.
Quick Answer: This question evaluates understanding of JWT structure, Base64URL encoding, string manipulation, and JSON parsing as applied to decoding token components. It is commonly asked to assess practical implementation abilities and edge-case/error handling in the Coding & Algorithms domain, emphasizing practical application over purely conceptual reasoning.