diff --git a/lib/rucio/core/authentication.py b/lib/rucio/core/authentication.py
index e8a0d6c7e5..0ddd81ac88 100644
--- a/lib/rucio/core/authentication.py
+++ b/lib/rucio/core/authentication.py
@@ -220,15 +220,20 @@ def get_auth_token_ssh(account, signature, appid, ip=None, *, session: "Session"
     The token lifetime is 1 hour.
 
     :param account: Account identifier as a string.
-    :param signature: Response to server challenge signed with SSH private key as string.
+    :param signature: Response to server challenge signed with SSH private key as a base64 encoded string.
     :param appid: The application identifier as a string.
     :param ip: IP address of the client as a string.
     :param session: The database session in use.
 
     :returns: A dict with token and expires_at entries.
     """
-    if not isinstance(signature, bytes):
-        signature = signature.encode()
+
+    # decode the signature which must come in base64 encoded
+    try:
+        signature += '=' * ((4 - len(signature) % 4) % 4)  # adding required padding
+        signature = b64decode(signature)
+    except TypeError:
+        raise CannotAuthenticate(f'Cannot authenticate to account {account} with malformed signature')
 
     # Make sure the account exists
     if not account_exists(account, session=session):
diff --git a/lib/rucio/web/rest/flaskapi/v1/auth.py b/lib/rucio/web/rest/flaskapi/v1/auth.py
index 70677b07a1..39915aa9c8 100644
--- a/lib/rucio/web/rest/flaskapi/v1/auth.py
+++ b/lib/rucio/web/rest/flaskapi/v1/auth.py
@@ -12,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import base64
 import json
 import logging
 import time
@@ -1215,18 +1214,6 @@ def get(self):
         appid = request.headers.get('X-Rucio-AppID', default='unknown')
         ip = request.headers.get('X-Forwarded-For', default=request.remote_addr)
 
-        # decode the signature which must come in base64 encoded
-        try:
-            signature += '=' * ((4 - len(signature) % 4) % 4)  # adding required padding
-            signature = base64.b64decode(signature)
-        except TypeError:
-            return generate_http_error_flask(
-                status_code=401,
-                exc=CannotAuthenticate.__name__,
-                exc_msg=f'Cannot authenticate to account {account} with malformed signature',
-                headers=headers
-            )
-
         try:
             result = get_auth_token_ssh(account, signature, appid, ip, vo=vo)
         except AccessDenied:
diff --git a/tests/test_authentication.py b/tests/test_authentication.py
index 9491c4632c..fbb98fb644 100644
--- a/tests/test_authentication.py
+++ b/tests/test_authentication.py
@@ -12,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import base64
 import datetime
 import time
 
@@ -125,7 +124,7 @@ def test_get_auth_token_ssh_success(self, vo, root_account):
 
         challenge_token = get_ssh_challenge_token(account='root', appid='test', ip='127.0.0.1', vo=vo).get('token')
 
-        signature = base64.b64decode(ssh_sign(PRIVATE_KEY, challenge_token))
+        signature = ssh_sign(PRIVATE_KEY, challenge_token)
 
         result = get_auth_token_ssh(account='root', signature=signature, appid='test', ip='127.0.0.1', vo=vo)
 
@@ -159,8 +158,7 @@ def test_invalid_padding(self, vo, root_account):
 
         challenge_token = get_ssh_challenge_token(account='root', appid='test', ip='127.0.0.1', vo=vo).get('token')
 
-        ssh_sign_string = ssh_sign(PRIVATE_KEY, challenge_token)
-        signature = base64.b64decode(ssh_sign_string)
+        signature = ssh_sign(PRIVATE_KEY, challenge_token)
         result = get_auth_token_ssh(account='root', signature=signature, appid='test', ip='127.0.0.1', vo=vo)
         assert result is not None