Subclass of SecretStr expects bytes as input

[AlexVndnblcke]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

For my use-case I have defined a subclass of the SecretStr type. This functionality worked fine in pydantic V1. Since the migration to V2 the follow error appeared continuously:

pydantic_core._pydantic_core.ValidationError: 1 validation error for [redacted]
shared_secret
  Input should be a valid bytes [type=bytes_type, input_value='[redacted]', input_type=str]

While the type is defined as follows:

class EncryptedBase64Str(SecretStr):
    def get_decrypted_value(self, aws_key_id: Union[str, UUID], **kwargs) -> str:
        decrypt_with_key(self.get_secret_value(), key=aws_key_id)

I.e. it is counter intuitive that the expected type is "bytes" when the class inherits from the specialized str variant.

This is due to the too restrictive test in pydantic.types._SecretFieldValidator.__get_pydantic_core_schema__ where type is evaluated based on the types defined by pydantic:

        self.inner_schema = handler(str if self.field_type is SecretStr else bytes)
        error_kind = 'string_type' if self.field_type is SecretStr else 'bytes_type'

Children of SecretStr are neglected here.

Example Code

from pydantic import SecretStr, ValidationError
from pydantic_settings import BaseSettings
from typing import Union
from uuid import UUID


class EncryptedBase64Str(SecretStr):
    def get_decrypted_value(self, aws_key_id: Union[str, UUID], **kwargs) -> str:
        # simplified for demonstration purposes
        return self.get_secret_value()


class Settings(BaseSettings):
    some_decryptable_secret: EncryptedBase64Str

try:
    Settings(some_decryptable_secret="abc")
except ValidationError as error:
    print(error)
    exit(0)

raise Exception("bug is not reproducible")

Python, Pydantic & OS Version

pydantic version: 2.0.3
        pydantic-core version: 2.3.0 release build profile
                 install path: /Users/alexandervandenbulcke/Library/Caches/pypoetry/virtualenvs/jarvis-api-5-3ao05Y-py3.9/lib/python3.9/site-packages/pydantic
               python version: 3.9.16 (main, Dec  7 2022, 10:02:13)  [Clang 14.0.0 (clang-1400.0.29.202)]
                     platform: macOS-12.5.1-arm64-arm-64bit
     optional deps. installed: ['typing-extensions']

Selected Assignee: @samuelcolvin