add dynamo sts handler

moto/dynamodb/urls.py

@@ -1,10 +1,38 @@
 from .responses import handler
 
 
+def sts_handler(uri, body, headers):
+    return GET_SESSION_TOKEN_RESULT
+
+
 url_bases = [
     "https?://dynamodb.us-east-1.amazonaws.com",
+    "https?://sts.amazonaws.com",
 ]
 
 url_paths = {
     "{0}/": handler,
 }
+
+
+GET_SESSION_TOKEN_RESULT = """
+<GetSessionTokenResponse xmlns="https://sts.amazonaws.com/doc/2011-06-15/">
+ <GetSessionTokenResult>
+ <Credentials>
+ <SessionToken>
+ AQoEXAMPLEH4aoAH0gNCAPyJxz4BlCFFxWNE1OPTgk5TthT+FvwqnKwRcOIfrRh3c/L
+ To6UDdyJwOOvEVPvLXCrrrUtdnniCEXAMPLE/IvU1dYUg2RVAJBanLiHb4IgRmpRV3z
+ rkuWJOgQs8IZZaIv2BXIa2R4OlgkBN9bkUDNCJiBeb/AXlzBBko7b15fjrBs2+cTQtp
+ Z3CYWFXG8C5zqx37wnOE49mRl/+OtkIKGO7fAE
+ </SessionToken>
+ <SecretAccessKey>
+ wJalrXUtnFEMI/K7MDENG/bPxRfiCYzEXAMPLEKEY
+ </SecretAccessKey>
+ <Expiration>2011-07-11T19:55:29.611Z</Expiration>
+ <AccessKeyId>AKIAIOSFODNN7EXAMPLE</AccessKeyId>
+ </Credentials>
+ </GetSessionTokenResult>
+ <ResponseMetadata>
+ <RequestId>58c5dbae-abef-11e0-8cfe-09039844ac7d</RequestId>
+ </ResponseMetadata>
+</GetSessionTokenResponse>"""