Create two users on the "test" db test> db.createUser({user: "testSha1", pwd: "passwordSha1", roles: [ Unknown macro: { role} , { role: 'dbAdmin', db: 'test' }], mechanisms: ['SCRAM-SHA-1'] }) Unknown macro: { ok} test> db.createUser({user: "testSha256", pwd: "passwordSha256", roles: [ Unknown macro: { role} , { role: 'dbAdmin', db: 'test' }], mechanisms: ['SCRAM-SHA-256'] }) Unknown macro: { ok} Run the application below: It simply commects to the Mongo server and attempts to authenticate using SCRAM-SHA algorithm. Notice that SCRAM-SHA-256 works as expected, but that SCRAM-SHA-1 generates an authentication failure. > python3 -m venv venv > source venv/bin/activate (venv) > pip install scramp (venv) > (venv) > (venv) > python3 mongo.py testSha256 passwordSha256 test SCRAM-SHA-256 AuthInit Reply:  r=a2f9b2678b0e410c8dfdb410459486dctCTAnXqb2b5XeJfgYQBahZpkvfwhhf8r,s=PblZy1gpLj6Jo4xn8jhqfrTlDL5vTvlgM4O1Hg==,i=15000 AuthCont Reply:  v=FK4U7vwRViyR/PuXzEE043ymUuojJdtz86NudnFCp1s= AuthFinal Reply: Looks Good (venv) > (venv) > (venv) >python3 mongo.py testSha1 passwordSha1 test SCRAM-SHA-1 AuthInit Reply:  r=b3b5d58b9f214115a9c2f5f26dabde30ZC8ZIDgk3Lr8YetZD+M9b9/hQJGjAIwX,s=5qobARF148RY4puhsQOkSg==,i=10000 b'a\x00\x00\x00\x01ok\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02errmsg\x00\x17\x00\x00\x00Authentication failed.\x00\x10code\x00\x12\x00\x00\x00\x02codeName\x00\x15\x00\x00\x00AuthenticationFailed\x00\x00' AuthCont: Reply not OK The following code is written in python to demonstrate the issue: Save this file as "mongo.py" This scripts sends an "AuthInit" followed by "AuthCont" followed by "AuthCont" objects to the mongo server. Reading the reply after each message to extract the "payload" to use in the SCRAM-SHA algorithm. It uses scamp a standard python module to generate the SCRAM-SHA messages. Authenticating with SCRAM-SHA-256 works fine.  Authenticating with SCRAM-SHA-1 fails. import socket import time import sys from scramp import ScramClient # Steps to run   > python3 -m venv venv   > source venv/bin/activate   > pip install scramp #   > python3 mongo.py def sendMessageGetPayload(mongo, data, message):     # mongo:        Socket connected to mongo server     # data:         bytearray of data to be sent to mongo     # message:      error message prefix.     #     # Send message to mongo     # Validate that it was sent.     size = len(data)     sent = mongo.send(data)     if size != sent:         print(bson)         sys.exit(message + ' Send failed: Sent: ' + str(sent) + ' of ' + str(size) + ' bytes')     #     # Retrieve the message from Mongo.     # The first 21 bytes is the header block.     # For simplicity just extracted the size.     reply = mongo.recv(21)     messageSize     = int.from_bytes(reply [0:4] , byteorder='little')     #     # Retrive the bson part of the essage.     # Do a simple check to make sure that the size is correct.     bson = mongo.recv(messageSize - 21)     bsonSize        = int.from_bytes(bson [0:4] , byteorder='little')     if messageSize != (bsonSize + 21):         print(bson)         sys.exit('AuthInit: Format Error:')     #     # Check the bson has an OK field     # And that field is a double with value 1.     findOk = bson.find(b'ok\x00')     if findOk == -1:         sys.exit(message + ' Failed to find OK')     if bson [findOk + 3: findOk + 3+ 8] != b'\x00\x00\x00\x00\x00\x00\xf0\x3f':         print(bson)         sys.exit(message + ' Reply not OK')     #     # If there is an OK field there should be a payload.     # So extract the payload from the bson     # The payload size is 4 bytes of the string payload.     # We ignore the 1 byte binary type.     findPayload = bson.find(b'payload\x00')     if findPayload == -1:         sys.exit(message + ' Could not find payload')     payloadSize     = int.from_bytes(bson [findPayload + 8:findPayload + 8 + 4] , byteorder='little')     payload         = bson [findPayload + 13:findPayload + 13 + payloadSize] .decode('ascii')     #     # Extract the conversionID as we need that for the reply.     findConvId = bson.find(b'conversationId\x00')     if findConvId == -1:         print(bson)         sys.exit(message + ' Could not find conversationId')     convId = int.from_bytes(bson [findConvId + 15: findConvId + 15 + 4] , byteorder='little')     return payload, convId def sendAuthInit(mongo, messageId, DBName, mech, firstMessage):     #     # Build the AuthInit Message in BSON by hand;     # Should look like this:     #   Unknown macro: {     #       saslStart}     authInit = bytearray()     bsonSize = 58 + len(mech) + 1 + len(firstMessage) + len(DBName) + 1     #     # Put the header in first.     authInit.extend(int(bsonSize +21).to_bytes(4, byteorder='little'))      #   MessageSize         193 => (21 Body + 172 BSON)     authInit.extend(int(messageId).to_bytes(4, byteorder='little'))         #   MessageId           1     authInit.extend(0x00.to_bytes(4, byteorder='little'))                   #   messageResponseId   0     authInit.extend(0x7DD.to_bytes(4, byteorder='little'))                  #   OPCode              OP_MSG     authInit.extend(0x00.to_bytes(4, byteorder='little'))                   #   Flags               0     authInit.extend(0x00.to_bytes(1, byteorder='little'))                   #   Kind                0     #     # BSON Object     authInit.extend(int(bsonSize).to_bytes(4, byteorder='little'))          #   Bson Size           172     authInit.extend(0x10.to_bytes(1, byteorder='little'));authInit.extend(b'saslStart\x00');authInit.extend(0x01.to_bytes(4, byteorder='little'))     authInit.extend(0x2.to_bytes(1, byteorder='little'));authInit.extend(b'mechanism\x00');authInit.extend(int(len(mech) + 1).to_bytes(4, byteorder='little'));authInit.extend(mech.encode('ascii'));authInit.extend(b'\x00')     authInit.extend(0x5.to_bytes(1, byteorder='little'));authInit.extend(b'payload\x00');authInit.extend(len(firstMessage).to_bytes(4, byteorder='little'));authInit.extend(0x0.to_bytes(1, byteorder='little'));authInit.extend(firstMessage.encode('ascii'))     authInit.extend(0x2.to_bytes(1, byteorder='little'));authInit.extend(b'$db\x00');authInit.extend(int(len(DBName) + 1).to_bytes(4, byteorder='little'));authInit.extend(DBName.encode('ascii'));authInit.extend(b'\x00')     authInit.extend(0x0.to_bytes(1, byteorder='little'))     #     # Send to mongo and get the import part of the reply     return sendMessageGetPayload(mongo, authInit, 'AuthInit:') def sendAuthContOne(mongo, messageId, DBName, conversationId, finalMessage):     #     # Build the AuthCont Message in BSON by hand;     # Should look like this:     #   Unknown macro: {     #       saslContinue}     authCont = bytearray()     bsonSize = 66 + len(DBName) + 1 + len(finalMessage)     #     # Put the header in first.     authCont.extend(int(bsonSize + 21).to_bytes(4, byteorder='little'))     #   MessageSize         196 => (21 Body + 175 BSON)     authCont.extend(int(messageId).to_bytes(4, byteorder='little'))         #   MessageId           2 or 3     authCont.extend(0x00.to_bytes(4, byteorder='little'))                   #   messageResponseId   0     authCont.extend(0x7DD.to_bytes(4, byteorder='little'))                  #   OPCode              OP_MSG     authCont.extend(0x00.to_bytes(4, byteorder='little'))                   #   Flags               0     authCont.extend(0x00.to_bytes(1, byteorder='little'))                   #   Kind                0     #     # BSON Object     authCont.extend(int(bsonSize).to_bytes(4, byteorder='little'))          #   Bson Size           175     authCont.extend(0x10.to_bytes(1, byteorder='little'));authCont.extend(b'saslContinue\x00');authCont.extend(0x01.to_bytes(4, byteorder='little'))     authCont.extend(0x10.to_bytes(1, byteorder='little'));authCont.extend(b'conversationId\x00');authCont.extend(conversationId.to_bytes(4, byteorder='little'))     authCont.extend(0x5.to_bytes(1, byteorder='little'));authCont.extend(b'payload\x00');authCont.extend(len(finalMessage).to_bytes(4, byteorder='little'));authCont.extend(0x0.to_bytes(1, byteorder='little'));authCont.extend(finalMessage.encode('ascii'))     authCont.extend(0x2.to_bytes(1, byteorder='little'));authCont.extend(b'$db\x00');authCont.extend(int(len(DBName) + 1).to_bytes(4, byteorder='little'));authCont.extend(DBName.encode('ascii'));authCont.extend(b'\x00')     authCont.extend(0x0.to_bytes(1, byteorder='little'))     #     # Send to mongo and get the import part of the reply     return sendMessageGetPayload(mongo, authCont, 'AuthCont:') def getUserInput():     if len(sys.argv) > 1:         username= sys.argv [1]     if len(sys.argv) > 2:         password= sys.argv [2]     if len(sys.argv) > 3:         DBName  = sys.argv [3]     if len(sys.argv) > 4:         mech    = sys.argv [4]     if username == '':         usernmae = input('Input username:  ')     if password == '':         password = input('Input password:  ')     if DBName == '':         DBName   = input('Input DB Name:   ')     if mech == '':         mech     = input('Input Mechanism: ')     if mech != 'SCRAM-SHA-1' and mech != 'SCRAM-SHA-256':         sys.exit('Invalid Mechanism: Use => "SCRAM-SHA-1" or "SCRAM-SHA-256"')     return username, password, DBName, mech username, password, DBName, mech = getUserInput() color: Color value is invalid # # Create socket HOST    = 'localhost' PORT    = 27017 mongo = socket.socket(socket.AF_INET, socket.SOCK_STREAM) mongo.connect((HOST,PORT)) #␣ Use library to generate SCRAM-SHA-X messages client = ScramClient( [mech] , username, password) # Send the first message to the server. authInitReply, conversationId1 = sendAuthInit(mongo, 1, DBName, mech, client.get_client_first()) print('AuthInit Reply: ', authInitReply) client.set_server_first(authInitReply) # Send the proof to the server. authContReply, conversationId2 = sendAuthContOne(mongo, 2, DBName, conversationId1, client.get_client_final()) client.set_server_final(authContReply) print('AuthCont Reply: ', authContReply) if conversationId1 != conversationId2:     sys.exit('AuthInit ConvId does not match AuthCont ConvId') # Send the OK we accept you are the server message authFinalReply, conversationId3 = sendAuthContOne(mongo, 3, DBName, conversationId2, '') print('AuthFinal Reply:', authFinalReply) if conversationId1 != conversationId3:     sys.exit('AuthInit ConvId does not match AuthFinal ConvId') # If no exceptions and no exit then Print Looks Good if authFinalReply != '':     sys.exit('AuthFinal Reply not empty!!!') print('Looks Good')   Helper script to print out the messages used in SCRAM-SHA-? communication. from scramp import ScramClient import base64 USERNAME = input('UserName (user)? ').strip() or 'user' PASSWORD = input('Password (pencil)? ').strip() or 'pencil' mech     = input('MECHANISMS (SCRAM-SHA-1)? ').strip() or 'SCRAM-SHA-1' Nonce    = input('Nonse Base64 encoded (fyko+d2lbbFgONRv9qkxdawL)? ').strip() or 'fyko+d2lbbFgONRv9qkxdawL' MECHANISMS = [mech] print() print() print('Username >' + USERNAME + '<') print('Password >' + PASSWORD + '<') print('Meachani >' + mech     + '<') print('Nonce    >' + Nonce    + '<') client = ScramClient(MECHANISMS, USERNAME, PASSWORD, channel_binding=None, c_nonce=Nonce) Get the client first message and send it to the server cfirst = client.get_client_first() print('Get Client First: >' + cfirst + '<') serverResponse = input('What is the server response?').strip() print() print('SR       >' + serverResponse + '<') client.set_server_first(serverResponse) cfinal = client.get_client_final() print('Get Client Final: result:          >' + cfinal + '<') serverResponse = input('What was the server response?') client.set_server_final(serverResponse) # If the server response is not correct it will throw an exception and thus never get here. print('All Good');