MUSUBI

```python
# Generated by MUSUBI - Automated Code Generator
# Specification: User authentication service with JWT tokens
# Language: Python 3.11
# Framework: FastAPI
# Style Guide: PEP 8
# Performance Criteria: <100ms response time for authentication

from fastapi import FastAPI, Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
from pydantic import BaseModel
from datetime import datetime, timedelta
from jose import JWTError, jwt
from passlib.context import CryptContext
import os

# Configuration
SECRET_KEY = os.getenv("SECRET_KEY", "your-secret-key-here")
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

# Password hashing
pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")

# Models
class Token(BaseModel):
    access_token: str
    token_type: str

class TokenData(BaseModel):
    username: str | None = None

class User(BaseModel):
    username: str
    email: str | None = None
    full_name: str | None = None
    disabled: bool | None = None

# Mock database
fake_users_db = {
    "johndoe": {
        "username": "johndoe",
        "full_name": "John Doe",
        "email": "johndoe@example.com",
        "hashed_password": pwd_context.hash("secret"),
        "disabled": False,
    }
}

app = FastAPI()

# Utility functions
def verify_password(plain_password: str, hashed_password: str):
    return pwd_context.verify(plain_password, hashed_password)

def get_password_hash(password: str):
    return pwd_context.hash(password)

def get_user(db, username: str):
    if username in db:
        user_dict = db[username]
        return User(**user_dict)
    return None

def authenticate_user(fake_db, username: str, password: str):
    user = get_user(fake_db, username)
    if not user:
        return False
    if not verify_password(password, user.hashed_password):
        return False
    return user

def create_access_token(data: dict, expires_delta: timedelta | None = None):
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.utcnow() + expires_delta
    else:
        expire = datetime.utcnow() + timedelta(minutes=15)
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt

# Authentication endpoints
@app.post("/token", response_model=Token)
async def login_for_access_token(form_data: OAuth2PasswordRequestForm = Depends()):
    user = authenticate_user(fake_users_db, form_data.username, form_data.password)
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Bearer"},
        )
    access_token_expires = timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
    access_token = create_access_token(
        data={"sub": user.username}, expires_delta=access_token_expires
    )
    return {"access_token": access_token, "token_type": "bearer"}

# User endpoints
@app.get("/users/me/", response_model=User)
async def read_users_me(token: str = Depends(OAuth2PasswordBearer(tokenUrl="token"))):
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = TokenData(username=username)
    except JWTError:
        raise credentials_exception
    user = get_user(fake_users_db, username=token_data.username)
    if user is None:
        raise credentials_exception
    return user

# Unit tests
import pytest
from fastapi.testclient import TestClient

client = TestClient(app)

def test_login_success():
    response = client.post(
        "/token",
        data={"username": "johndoe", "password": "secret"}
    )
    assert response.status_code == 200
    assert "access_token" in response.json()

def test_login_failure():
    response = client.post(
        "/token",
        data={"username": "johndoe", "password": "wrongpassword"}
    )
    assert response.status_code == 401

def test_get_current_user():
    # First get a token
    token_response = client.post(
        "/token",
        data={"username": "johndoe", "password": "secret"}
    )
    token = token_response.json()["access_token"]
    
    # Then use the token to get user info
    response = client.get("/users/me/", headers={"Authorization": f"Bearer {token}"})
    assert response.status_code == 200
    assert response.json()["username"] == "johndoe"
```