cmdbuild webservice create relation 接口调用返回401

[N32_pangyue]

使用cmdbuild遇到接口调用问题。
cmdbuild版本：2.5.1
jdk：1.8.0_191
tomcat：8.5.34
postgresql：9.4.10

脚本使用python编写，以下为接口调用部分。
#encoding:utf-8
import requests
class REQ:
def __init__(self):
self.server = 'xx.xx.xx.xx:8080'
self.sessions_url="http://%s/cmdbuild/services/rest/v2/sessions" % self.server
self.relations_url="http://"+self.server+"/cmdbuild/services/rest/v2/domains/%s/relations"
res = requests.post(self.sessions_url,data='{"username":"admin","password":"admin"}', headers={'Content-Type': 'application/json'})
self.session = res.json()["data"]["_id"]
self.headers={'CMDBuild-Authorization': self.session, 'Content-Type': 'application/json'}

def create_relation(self,d,data):
print((self.relations_url % d))
res=requests.post(self.relations_url % d,headers=data)
return res

def get_session(self,c):
res=requests.get(self.get_se % c,headers=self.headers)
json_data=res.json()
return json_data


if __name__ == '__main__':
req = REQ()
source_id='2106'
data = {
'_destinationId': '75',
'_destinationType': 'loadbalancer',
'_sourceType': 'wzh',
'_sourceId': source_id ,
'DefaultGroup' : 'false'
}
print req.create_relation('183wzhAPP',data)

调用后，返回401
cmdbuild的日志文件cmdbuild.log中有如下信息
INFO 2018-12-04 09:08:20 [cmdbuild] trying to login user admin with group null
DEBUG 2018-12-04 09:08:20 [cmdbuild] request received for '/services/rest/v2/sessions/g3o2rk8bucndb9i2861jjoupr0'
DEBUG 2018-12-04 09:08:20 [cmdbuild] request received for '/services/rest/v2/domains/183wzhAPP/relations'

尝试了更换用户，添加相应的组，使用类型为normal,adminitrator,limited administrator，也尝试了在normal下修改permission为write。但是调用该脚本返回均为401。
请大家给看下如何解决