Migrating from firebase to auth0 - firebase-authentication

Question

I'm trying to convert from firebase into an auth0 db, by converting firebase export data into the auth0 bulk user import format.
I have a user in firebase (under the firebase_export) section, and the firebase hash config itself (hash config below),
but I'm not clear on how the base64_signer_key fits in or the salt used in the export.
{
"firebase_export": {
"localId": "localId",
"email": "e#ma.il",
"emailVerified": true,
"passwordHash": "base64hash",
"salt": "user_salt",
"lastSignedInAt": "1649680364736",
"createdAt": "1649680237223",
"disabled": false,
"providerUserInfo": []
},
"hash_config": {
"algorithm": "SCRYPT",
"base64_signer_key": "base64_signer_key",
"base64_salt_separator": "base64_salt_separator",
"rounds": 8,
"mem_cost": 14
}
}
I think the schema should look like this, but this is not working.
(I log in to auth0 with a known password and it fails, while passing in firebase).
[
{
"user_id": $localId,
"email": $email,
"email_verified": $emailVerified,
"custom_password_hash": {
"algorithm": "scrypt",
"hash": {
"value": $passwordHash,
"encoding": "base64"
},
"salt" : {
"value": base64Decode($salt) + base64Decode($hash_config.base64_salt_separator),
// based off reading https://github.com/firebase/scrypt
"encoding":"utf8",
"position" "suffix", // based off reading https://github.com/firebase/scrypt, uses PBKDF2_SHA256 which places salt as suffix.
},
"password" : {
"encoding":"utf8"
},
"keylen": 64,
"cost": 2**$hash_config.mem_cost,
"blockSize": $hash_config.rounds,
"parallelization": 1,
},
"blocked": $disabled
}
]

Answer 1

Because Firebase uses a custom bcrypt rather than the standard implementation, auth0 said it is unable to import users.
Other solutions to try:
add a login callback within your code to create/update/delete users in auth0 in an async fashion, to slowly migrate users over.
pay auth0 lots of money to run a custom db migration (still slow).
migrate all users without password and say that we need all users to reset their password
all of which sound suboptimal