client: allow injecting a requests.Session + stop following redirects

The HTTP Session was hardcoded with no injection point and followed
redirects by default, so a server-side caller pointing the client at an
attacker-influenced base_url (a tenant's prime_endpoint) had no way to
attach an SSRF policy, and a public endpoint could 302-redirect the
request to an internal address (e.g. the cloud metadata service).

- Client/DragonchainSDK now accept an optional `session` so callers can
  inject a Session whose transport adapter refuses internal IPs. Default
  stays unguarded for trusted/CLI use — the guard belongs in the server.
- Requests are sent with allow_redirects=False; Prime never legitimately
  redirects, and a 3xx now surfaces to the caller instead of being followed.

prime_sdk/client.py

@@ -39,13 +39,20 @@ class Client:
         auth_key: str,
         base_url: str,
         timeout: int = DEFAULT_TIMEOUT,
+        session: Optional[requests.Session] = None,
     ):
         self.public_id = public_id
         self.auth_key_id = auth_key_id
         self.auth_key = auth_key
         self.base_url = base_url.rstrip("/")
         self.timeout = timeout
-        self._session = requests.Session()
+        # A caller may inject a pre-configured Session — e.g. one with a
+        # transport adapter that refuses to connect to internal IPs — when the
+        # base_url is attacker-influenced (a tenant's prime_endpoint). The
+        # default Session is unguarded, which is fine for trusted/CLI use; the
+        # SSRF policy belongs in the server that points this client at
+        # untrusted endpoints, not baked into the client library.
+        self._session = session if session is not None else requests.Session()
 
     # -- introspection helpers (mirror the Go accessors) --------------------
 
@@ -120,8 +127,17 @@ class Client:
             headers["Content-Type"] = content_type
 
         url = self.base_url + path
+        # allow_redirects=False: Prime is a JSON API that never legitimately
+        # 3xx-redirects, and following redirects is an SSRF vector (a public
+        # endpoint that 302s to an internal address). A redirect surfaces as a
+        # 3xx the caller can inspect rather than being silently followed.
         resp = self._session.request(
-            method, url, data=body_bytes, headers=headers, timeout=self.timeout
+            method,
+            url,
+            data=body_bytes,
+            headers=headers,
+            timeout=self.timeout,
+            allow_redirects=False,
         )
 
         resp_text = resp.text