Forem: Roy

What is JWT? how to create one?

Roy — Sun, 11 Aug 2019 11:48:55 +0000

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA.

What is the JSON Web Token structure?

In its compact form, JSON Web Tokens consist of three parts separated by dots (.), which are:
Header
Payload
Signature

Therefore, a JWT typically looks like the following.
xxxxx.yyyyy.zzzzz

Let's break down the different parts.

Header
The header typically consists of two parts: the type of the token, which is JWT, and the signing algorithm being used, such as HMAC SHA256 or RSA.

For example:

{
"alg": "HS256",
"typ": "JWT"
}
Then, this JSON is Base64Url encoded to form the first part of the JWT.

Payload
The second part of the token is the payload, which contains the claims. Claims are statements about an entity (typically, the user) and additional data. There are three types of claims: registered, public, and private claims.

Registered claims: These are a set of predefined claims which are not mandatory but recommended, to provide a set of useful, interoperable claims. Some of them are: iss (issuer), exp (expiration time), sub (subject), aud (audience), and others.

Notice that the claim names are only three characters long as JWT is meant to be compact.

Public claims: These can be defined at will by those using JWTs. But to avoid collisions they should be defined in the IANA JSON Web Token Registry or be defined as a URI that contains a collision resistant namespace.

Private claims: These are the custom claims created to share information between parties that agree on using them and are neither registered or public claims.

An example payload could be:

{
"sub": "1234567890",
"name": "John Doe",
"admin": true
}
The payload is then Base64Url encoded to form the second part of the JSON Web Token.

Do note that for signed tokens this information, though protected against tampering, is readable by anyone. Do not put secret information in the payload or header elements of a JWT unless it is encrypted.

Signature
To create the signature part you have to take the encoded header, the encoded payload, a secret, the algorithm specified in the header, and sign that.

For example if you want to use the HMAC SHA256 algorithm, the signature will be created in the following way:

HMACSHA256(
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
secret)
The signature is used to verify the message wasn't changed along the way, and, in the case of tokens signed with a private key, it can also verify that the sender of the JWT is who it says it is.

Note that JWT is not encryption method but digital signature.

More info about JWT: jwt.io

So we understood what is JWT..
For using it you will need to implement JWT receiving in your API.

Today we will see how to create the JWT itself..

Python have dedicated library for that.
*** Let's get started! ***

Install PyJWT.

pip install pyjwt

Import it.

import jwt

Create a payload

payload = {"userId":1234}

Define your secret

secret= [your secret key]

Define JWT encryption algorithm (optional).

JWT_ALGORITHM = "HS256"

Encode.

jwtToken = jwt.encode(payload, secret, JWT_ALGORITHM)

Put it all together:

import jwt

payload = {"userId":1234}
secret= "secret"
JWT_ALGORITHM = "HS256"

jwtToken = jwt.encode(payload, secret, JWT_ALGORITHM)
print(jwtToken)

Enjoy :)

Automate your computer- remove emails

Roy — Sun, 30 Jun 2019 05:17:24 +0000

So I encountered a really annoying problem at my work.
We have support auto-emails and they send me to much emails.

What most people would do in this situation? make a rule to put it in a different folder.
So now I have 300,000+ emails their and I can not enter to the folder, the outlook is crushing... what should we do?

Lets write a script that delete our emails.

For that we will use imaplib library.

import imaplib

We also will use datetime so:

import datetime

Next we need a new class..

class EmailCleaner:
    def deleteEmail(self):
        imap_host = 'imap-mail.outlook.com' # for gmail please use: 'imap.gmail.com'
        mail = imaplib.IMAP4_SSL(imap_host)
        mail.login('your email', 'your password')

We created a new class called "EmailCleaner", inside we create new method called "deleteEmail".
The next 3 lines define the host (outlook in my example), open SSL connection and preform login to your email.

After we logged-in lets select the required folder and start running on it.
For that we need to get the folder name and how many days (my deafult is 50) we want to go throw.

class EmailCleaner:
    def deleteEmail(self, folderName, daysBack = 50):
        imap_host = 'imap-mail.outlook.com'
        mail = imaplib.IMAP4_SSL(imap_host) 
        mail.login('your email', 'your password')
        mail.select(mailbox=folderName, readonly=False)

        for i in range(0, daysBack):
            date = (datetime.date.today() - datetime.timedelta(i)).strftime("%d-%b-%Y")
            result, data = mail.search(None, '(SENTSINCE {0})'.format(date))

We just selected the requested folder via mail.select and put readonly=false cause we want to remove it.

By default we can not get all the email, but only in batches (~1000), so I created a loop on the days and it will remove the emails depend on the day.
Then I searched for the requested emails by date- "SENTSINCE".
For other queries you can read here: RFC

 for num in data[0].split():
     mail.store(num, '+FLAGS', r'(\Deleted)')
     print(f'adding email {num} to remove list...')

I created nested loop, and mark every email with delete flag.

So we did login, selected a folder and run in for loop on that folder, get the emails by date and mark them with deleted flag, now it's time for delete the emails.

For delete the emails we will use this:

mail.expunge()

Let's check out all the code (I added some prints)...

def deleteEmail(self, folderName, daysBack = 50):
    mail = imaplib.IMAP4_SSL(imap_host)
        mail.login('your email', 'your password')

    print("Login success")
    mail.select(mailbox=folderName, readonly=False)

    for i in range(0, daysBack):
        date = (datetime.date.today() - datetime.timedelta(i)).strftime("%d-%b-%Y")
        result, data = mail.search(None, '(SENTSINCE {0})'.format(date))

        for num in data[0].split():
            mail.store(num, '+FLAGS', r'(\Deleted)') #change flag to delete
            print(f'adding email {num} to remove list...')
        mail.expunge() # delete the emails
        print(f'Emails back from day: {i} removed.')
        # close connection and logout
    mail.close()
    mail.logout()

It's almost ready! now lets add try\catch now handle exceptions.

    def deleteEmail(self, folderName, daysBack = 50):
        try:
            mail = imaplib.IMAP4_SSL(imap_host)
            mail.login('your email', 'your password')

            print("Login success")
            mail.select(mailbox=folderName, readonly=False)

            for i in range(0, daysBack):
                date = (datetime.date.today() - datetime.timedelta(i)).strftime("%d-%b-%Y")
                result, data = mail.search(None, '(SENTSINCE {0})'.format(date))

                for num in data[0].split():
                    mail.store(num, '+FLAGS', r'(\Deleted)')
                    print(f'adding email {num} to remove list...')
                mail.expunge()
                print(f'Emails back from day: {i} removed.')
            mail.close()
            mail.logout()
        except Exception as e:
            raise Exception(f'Unable to delete emails, e.')

If you want to start it via the console, you can add console interface with Fire.
You can out my post how to implement that: Automatically generate command line interfaces

*Enjoy :) *

Automatically generate command line interfaces

Roy — Tue, 25 Jun 2019 08:25:49 +0000

Hey Guys!
I would like to introduce you a very useful library written by Google!

With Fire package, you can generate very easily command line interfaces automatically.

Check it out here:
https://github.com/google/python-fire

Enjoy :)

Watermark batch of images

Roy — Mon, 24 Jun 2019 11:03:09 +0000

Hey all!
Let's assume you have a lot of images and you want to watermark all of them.
There are some online website that doing that, but when we are talking about a lot (for example 5000) of images this may be very slow.

So I thought to myself- why no to automate that?

I publish it as python package.
You can find the source code and "how to" guide here:
https://github.com/roybs2/watermark-image

Any comments, new ideas will be blessed.

Thanks and have a great week! :)