diff --git a/docs/guides/error-handling.md b/docs/guides/error-handling.md
index 9b13aacb..9457f2d2 100644
--- a/docs/guides/error-handling.md
+++ b/docs/guides/error-handling.md
@@ -10,6 +10,7 @@ OtfError
 │   └── RetryableOtfRequestError
 ├── OtfAuthenticationError
 ├── OtfTransportError
+├── OtfConfigurationError
 ├── BookingError
 │   ├── AlreadyBookedError
 │   ├── ConflictingBookingError
@@ -30,6 +31,7 @@ from otf_api.exceptions import (
     RetryableOtfRequestError,
     OtfAuthenticationError,
     OtfTransportError,
+    OtfConfigurationError,
     BookingError,
     AlreadyBookedError,
     ConflictingBookingError,
@@ -112,6 +114,21 @@ except OtfTransportError as e:
     # The original httpx exception is available as e.__cause__
 ```
 
+### OtfConfigurationError
+
+Raised when the underlying boto3/botocore client is misconfigured or invoked with invalid parameters — for example, an invalid `AWS_PROFILE` or a parameter validation failure. Unlike `OtfTransportError`, these failures are not retryable: retrying won't fix a bad configuration. Wraps the underlying `botocore` error so consumers don't need to import `botocore`.
+
+```python
+from otf_api import OtfUser
+from otf_api.exceptions import OtfConfigurationError
+
+try:
+    user = OtfUser(username="user@example.com", password="correct")
+except OtfConfigurationError as e:
+    print(f"Configuration error: {e}")
+    # The original botocore.exceptions.BotoCoreError is available as e.__cause__
+```
+
 ### BookingError
 
 Base class for all booking-related errors. Carries identifiers for the affected booking.
diff --git a/src/otf_api/auth/auth.py b/src/otf_api/auth/auth.py
index ad4e327e..6f084ebf 100644
--- a/src/otf_api/auth/auth.py
+++ b/src/otf_api/auth/auth.py
@@ -6,7 +6,7 @@
 from functools import cached_property
 from logging import getLogger
 from time import sleep
-from typing import Any, ClassVar
+from typing import Any, ClassVar, NoReturn
 
 import httpx
 import jwt
@@ -16,12 +16,18 @@
 from botocore.awsrequest import AWSRequest
 from botocore.config import Config
 from botocore.credentials import Credentials
-from botocore.exceptions import ClientError
+from botocore.exceptions import BotoCoreError, ClientError, HTTPClientError
+from botocore.exceptions import ConnectionError as BotoConnectionError
 from pycognito import AWSSRP, Cognito
 from pycognito.aws_srp import generate_hash_device
 
 from otf_api.cache import get_cache
-from otf_api.exceptions import NoCredentialsError, OtfAuthenticationError
+from otf_api.exceptions import (
+    NoCredentialsError,
+    OtfAuthenticationError,
+    OtfConfigurationError,
+    OtfTransportError,
+)
 
 if typing.TYPE_CHECKING:
     from mypy_boto3_cognito_identity import CognitoIdentityClient
@@ -40,6 +46,33 @@
 CACHE = get_cache()
 
 
+def raise_for_botocore_error(e: BotoCoreError, action: str) -> NoReturn:
+    """Log and re-raise a caught BotoCoreError as the correct public Otf* exception.
+
+    ClientError is a sibling of BotoCoreError, not a subclass, so this is never called for
+    API-level failures. ConnectionError and HTTPClientError are the two transport-failure
+    branches of BotoCoreError's hierarchy (connectivity, timeout, failure to reach an
+    already-resolved endpoint) — genuinely retryable, so they're reported as
+    OtfTransportError. Everything else under BotoCoreError (ParamValidationError,
+    ProfileNotFound, NoRegionError, etc.) is a configuration/validation failure that a
+    retry cannot fix, so it's reported as OtfConfigurationError.
+
+    Args:
+        e: The caught BotoCoreError.
+        action: Present-tense description of what was happening, for the log message
+            (e.g. "authenticating with Cognito").
+
+    Raises:
+        OtfTransportError: If e is a connectivity, timeout, or endpoint-connection failure.
+        OtfConfigurationError: If e is any other BotoCoreError.
+    """
+    if isinstance(e, BotoConnectionError | HTTPClientError):
+        LOGGER.exception("Transport error while %s", action)
+        raise OtfTransportError("OTF transport error") from e
+    LOGGER.exception("Configuration error while %s", action)
+    raise OtfConfigurationError("OTF configuration error") from e
+
+
 class OtfCognito(Cognito):
     """A subclass of the pycognito Cognito class that adds the device_key to the auth_params.
 
@@ -319,6 +352,9 @@ def check_token(self, renew: bool = True) -> bool:
         Raises:
             AttributeError: If access_token is not set
             NoCredentialsError: If refresh token has expired
+            OtfAuthenticationError: If token refresh fails for another Cognito-reported reason
+            OtfTransportError: If a connectivity, timeout, or endpoint failure occurs during refresh
+            OtfConfigurationError: If a boto3/botocore configuration or validation failure occurs during refresh
 
         Returns:
             bool: True if the access_token has expired, False otherwise
@@ -330,7 +366,10 @@ def check_token(self, renew: bool = True) -> bool:
                 LOGGER.warning("Tokens expired, attempting to login with username and password")
                 CACHE.clear()
                 raise NoCredentialsError("Cached tokens expired, please login again") from e
-            raise OtfAuthenticationError(str(e)) from e
+            LOGGER.exception("Failed to refresh Cognito tokens")
+            raise OtfAuthenticationError("OTF authentication failed") from e
+        except BotoCoreError as e:
+            raise_for_botocore_error(e, "refreshing Cognito tokens")
 
     def renew_access_token(self) -> None:
         """Sets a new access token on the User using the cached refresh token and device metadata.
diff --git a/src/otf_api/auth/user.py b/src/otf_api/auth/user.py
index 1c8acafd..b7341b72 100644
--- a/src/otf_api/auth/user.py
+++ b/src/otf_api/auth/user.py
@@ -1,9 +1,9 @@
 from logging import getLogger
 
 import attrs
-from botocore.exceptions import ClientError
+from botocore.exceptions import BotoCoreError, ClientError
 
-from otf_api.auth.auth import HttpxCognitoAuth, OtfCognito
+from otf_api.auth.auth import HttpxCognitoAuth, OtfCognito, raise_for_botocore_error
 from otf_api.auth.utils import get_username_password
 from otf_api.exceptions import NoCredentialsError, OtfAuthenticationError
 
@@ -27,7 +27,9 @@ def _create_cognito(username: str | None, password: str | None, **kwargs: str |
         raise
     except ClientError as e:
         _log_initial_auth_error(e, username)
-        raise OtfAuthenticationError(str(e)) from e
+        raise OtfAuthenticationError("OTF authentication failed") from e
+    except BotoCoreError as e:
+        raise_for_botocore_error(e, "authenticating with Cognito")
     except Exception:
         LOGGER.exception("Failed to authenticate with Cognito")
         raise
diff --git a/src/otf_api/exceptions.py b/src/otf_api/exceptions.py
index 2d96d583..a78a8e68 100644
--- a/src/otf_api/exceptions.py
+++ b/src/otf_api/exceptions.py
@@ -12,6 +12,7 @@
     "ConflictingBookingError",
     "NoCredentialsError",
     "OtfAuthenticationError",
+    "OtfConfigurationError",
     "OtfError",
     "OtfRequestError",
     "OtfTransportError",
@@ -100,5 +101,14 @@ class OtfTransportError(OtfError):
     """
 
 
+class OtfConfigurationError(OtfError):
+    """Raised when the boto3/botocore client is misconfigured or invoked with invalid parameters.
+
+    Covers non-network BotoCoreError failures (e.g. a missing AWS profile, an unresolvable region,
+    or a parameter validation error) that a retry cannot fix. The original error is available via
+    ``__cause__``.
+    """
+
+
 class NoCredentialsError(OtfError):
     """Raised when no credentials are provided and no cached tokens are available."""
diff --git a/tests/test_api/test_errors.py b/tests/test_api/test_errors.py
index 0e6157c6..66c874aa 100644
--- a/tests/test_api/test_errors.py
+++ b/tests/test_api/test_errors.py
@@ -6,11 +6,17 @@
 import httpx
 import pytest
 import respx
-from botocore.exceptions import ClientError
+from botocore.exceptions import ClientError, EndpointConnectionError, ParamValidationError
 
 from otf_api.api.client import API_BASE_URL, OtfClient
 from otf_api.auth.user import OtfUser
-from otf_api.exceptions import NoCredentialsError, OtfAuthenticationError, OtfError, OtfTransportError
+from otf_api.exceptions import (
+    NoCredentialsError,
+    OtfAuthenticationError,
+    OtfConfigurationError,
+    OtfError,
+    OtfTransportError,
+)
 
 
 def _make_client_error(code: str = "NotAuthorizedException", message: str = "bad creds") -> ClientError:
@@ -51,6 +57,17 @@ def cognito_side_effect(**kwargs: object) -> Never:
 
         assert exc_info.value.__cause__ is error
 
+    def test_auth_error_message_is_fixed_and_safe(self):
+        error = _make_client_error(message="secret provider detail")
+        with (
+            patch("otf_api.auth.user.OtfCognito", side_effect=error),
+            pytest.raises(OtfAuthenticationError) as exc_info,
+        ):
+            OtfUser(username="test@example.com", password="wrong")
+
+        assert str(exc_info.value) == "OTF authentication failed"
+        assert "secret provider detail" not in str(exc_info.value)
+
     def test_auth_error_is_subclass_of_otf_error(self):
         assert issubclass(OtfAuthenticationError, OtfError)
 
@@ -94,3 +111,30 @@ def test_read_error_raises_transport_error(self, mock_user):
 
     def test_transport_error_is_subclass_of_otf_error(self):
         assert issubclass(OtfTransportError, OtfError)
+
+    def test_construction_time_connectivity_failure_raises_transport_error(self):
+        error = EndpointConnectionError(endpoint_url="https://cognito-idp.example.com")
+        with (
+            patch("otf_api.auth.user.OtfCognito", side_effect=error),
+            pytest.raises(OtfTransportError) as exc_info,
+        ):
+            OtfUser(username="test@example.com", password="wrong")
+
+        assert str(exc_info.value) == "OTF transport error"
+        assert exc_info.value.__cause__ is error
+
+
+class TestOtfConfigurationError:
+    def test_construction_time_config_failure_raises_configuration_error(self):
+        error = ParamValidationError(report="bad params")
+        with (
+            patch("otf_api.auth.user.OtfCognito", side_effect=error),
+            pytest.raises(OtfConfigurationError) as exc_info,
+        ):
+            OtfUser(username="test@example.com", password="wrong")
+
+        assert str(exc_info.value) == "OTF configuration error"
+        assert exc_info.value.__cause__ is error
+
+    def test_configuration_error_is_subclass_of_otf_error(self):
+        assert issubclass(OtfConfigurationError, OtfError)
diff --git a/tests/test_auth/test_otf_cognito.py b/tests/test_auth/test_otf_cognito.py
index b89f3aa4..7b47a63d 100644
--- a/tests/test_auth/test_otf_cognito.py
+++ b/tests/test_auth/test_otf_cognito.py
@@ -3,9 +3,10 @@
 from unittest.mock import MagicMock, PropertyMock, patch
 
 import pytest
-from botocore.exceptions import ClientError
+from botocore.exceptions import ClientError, EndpointConnectionError, ParamValidationError
 
 from otf_api.auth.auth import NoCredentialsError, OtfCognito
+from otf_api.exceptions import OtfAuthenticationError, OtfConfigurationError, OtfTransportError
 
 from .conftest import fake_tokens
 
@@ -231,6 +232,64 @@ def test_check_token_not_authorized(mock_cache, mock_verify_token):
     mock_clear.assert_called_once()
 
 
+def test_check_token_other_client_error_raises_auth_error(mock_cache, mock_verify_token):
+    """check_token raises OtfAuthenticationError with a fixed, safe message for non-auth-expiry ClientErrors."""
+    mock_cache.write_token_data_to_cache({"access_token": _ACCESS_TOKEN, "id_token": "id", "refresh_token": "rt"})
+    mock_cache.write_device_data_to_cache({"device_key": "dk", "device_group_key": "dgk", "device_password": "dp"})
+
+    with patch("pycognito.Cognito.check_token", return_value=False):
+        cognito = OtfCognito(username="user@test.com")
+
+    error = _client_error("InternalErrorException", message="secret provider detail")
+    with (
+        patch("pycognito.Cognito.check_token", side_effect=error),
+        pytest.raises(OtfAuthenticationError) as exc_info,
+    ):
+        cognito.check_token()
+
+    assert str(exc_info.value) == "OTF authentication failed"
+    assert "secret provider detail" not in str(exc_info.value)
+    assert exc_info.value.__cause__ is error
+
+
+def test_check_token_connectivity_failure_raises_transport_error(mock_cache, mock_verify_token):
+    """check_token raises OtfTransportError with a fixed, safe message on refresh-time connectivity failures."""
+    mock_cache.write_token_data_to_cache({"access_token": _ACCESS_TOKEN, "id_token": "id", "refresh_token": "rt"})
+    mock_cache.write_device_data_to_cache({"device_key": "dk", "device_group_key": "dgk", "device_password": "dp"})
+
+    with patch("pycognito.Cognito.check_token", return_value=False):
+        cognito = OtfCognito(username="user@test.com")
+
+    error = EndpointConnectionError(endpoint_url="https://cognito-idp.example.com")
+    with (
+        patch("pycognito.Cognito.check_token", side_effect=error),
+        pytest.raises(OtfTransportError) as exc_info,
+    ):
+        cognito.check_token()
+
+    assert str(exc_info.value) == "OTF transport error"
+    assert exc_info.value.__cause__ is error
+
+
+def test_check_token_configuration_error_raises_configuration_error(mock_cache, mock_verify_token):
+    """check_token raises OtfConfigurationError with a fixed, safe message on non-transport BotoCoreErrors."""
+    mock_cache.write_token_data_to_cache({"access_token": _ACCESS_TOKEN, "id_token": "id", "refresh_token": "rt"})
+    mock_cache.write_device_data_to_cache({"device_key": "dk", "device_group_key": "dgk", "device_password": "dp"})
+
+    with patch("pycognito.Cognito.check_token", return_value=False):
+        cognito = OtfCognito(username="user@test.com")
+
+    error = ParamValidationError(report="bad params")
+    with (
+        patch("pycognito.Cognito.check_token", side_effect=error),
+        pytest.raises(OtfConfigurationError) as exc_info,
+    ):
+        cognito.check_token()
+
+    assert str(exc_info.value) == "OTF configuration error"
+    assert exc_info.value.__cause__ is error
+
+
 # ---------------------------------------------------------------------------
 # Subtask 12 — _set_tokens happy path
 # ---------------------------------------------------------------------------