Updating Doc for Pomerium-Dex Exercise (#2018)

* Updating Doc for Pomerium-Dex Exercise

This PR has Documentation for Pomerium-Dex Integration.

Please let me know the changes or do the needful.

I can refactor this.

* Removing Last Two Lines

* Update readme.md

docs/docs/identity-providers/readme.md

@@ -31,3 +31,169 @@ You must configure an IdP **[Service Account]** to write policy against group me
 [openid connect]: https://en.wikipedia.org/wiki/OpenID_Connect
 [service account]: ../../reference/readme.md#identity-provider-service-account
 
+
+### Pomerium-Dex-Freeipa Exercise
+
+**This exercise depicts the authentication flow for the services which don't have authentication flow**
+
+*Flow with the diagram*
+
+![alt text](https://github.com/dharmendrakariya/pomerium-dex/blob/main/image.jpg?raw=true)
+
+
+1. User makes an unauthenticated request to the service
+
+2. Pomerium proxy receives the request and recognizes it as anonymous
+
+3. It redirects the user to the auth provider for authentication
+
+4. Upon successful login, Pomerium provides an auth cookie to the user.
+
+5. Based on the cookie, Pomerium identifies the user and checks policy to determine whether to permit access. Authorization is based on identity factors like id, email,      group, role, or email domain.
+
+6. When the cookie expires, the login flow gets triggered all over again.
+
+
+*Here is our flow for accessing nextcloud service*
+
+1. User access https://hello.YOURDOMAIN.dev
+
+2. It will be redirected to the https://authenticate.YOURDOMAIN.dev (which is pomerium's authenticate service url)
+
+3. Pomerium's authenticate service will redirect this to check at oidc provider( in our case DEX).
+
+4. Dex(which is backed by FreeIpa in our case, freeipa's LDAP as backend) will check if the user is valid or not and after that flow gets redirected to pomerium back if user is valid.
+
+5. User is finally redirected to the nextcloud service if all goes well.
+
+
+Now to implement this flow we have configured static dex client ```pom``` with pomerium's authenticate service redirectURL
+
+```Note: I am using dex helm chart and in backend freeipa as a ldap server```
+
+```
+connectors:
+      - config:
+          bindDN: uid=dex,cn=sysaccounts,cn=etc,dc=YOURDOMAIN,dc=dev
+          bindPW: mN****tG****
+          host: freeipa.YOURDOMAIN.dev:636
+          insecureNoSSL: false
+          insecureSkipVerify: true
+
+          # (Group Search )
+          groupSearch:
+            baseDN: cn=groups,cn=accounts,dc=YOURDOMAIN,dc=dev
+            filter: "(|(objectClass=posixGroup)(objectClass=group))"
+            userAttr: DN # Use "DN" here not "uid"
+            groupAttr: member
+            nameAttr: cn
+
+          # (User Search)
+          userSearch:
+            baseDN: cn=users,cn=accounts,dc=YOURDOMAIN,dc=dev
+            emailAttr: mail
+            filter: ""
+            idAttr: uidNumber
+            nameAttr: displayName
+            preferredUsernameAttr: uid
+            username: mail
+          usernamePrompt: Email
+        id: ldap
+        name: FreeIPA/LDAP
+        type: ldap
+      issuer: http://dex.YOURDOMAIN.dev
+      logger:
+        level: debug
+      oauth2:
+        responseTypes:
+        - code
+        skipApprovalScreen: false
+
+      staticClients:
+      # (Here I am creating static client for pomerium)
+      - id: pom
+        name: pom
+        redirectURIs:
+        # (pomerium authenticate service url)
+        - https://authenticate.YOURDOMAIN.dev/oauth2/callback
+        secret: pomerium
+
+```
+Below is configuration which supposed to be done in Pomerium
+
+```Note: I am using Pomerium helm chart```
+
+```
+config:
+  # routes under this wildcard domain are handled by pomerium
+  rootDomain: YOURDOMAIN.dev
+
+  policy:
+      # (give any name instead of hello, this will be the proxy url to access the particular service)
+    - from: https://hello.YOURDOMAIN.dev
+      # (give fqdn of the actual service which is being authenticated, here I am giving nextcloud service endpoint, which is running in nextcloud namespace)
+      to: http://nextcloud.nextcloud.svc.cluster.local:8080
+
+      # allowed_domains:
+          #(in general give here your domain)
+      #   - YOURDOMAIN.dev
+
+      # (If you want to give access to particular group members, I have tested this by creating devops group and members in that group, in freeipa)
+      allowed_groups:
+        - devops
+
+      # (If you want to give access to particular group members, I have tested this by creating devops group and members in that group, in freeipa)
+      allowed_idp_claims:
+        groups:
+        - devops
+
+  # (I didn't specify the root level CAs so)
+  insecure: true
+
+extraEnv:
+  # (This will give you details if user is not able to authenticate, ideally this should be turned off)
+  POMERIUM_DEBUG: true
+  LOG_LEVEL: "error"
+  IDP_SCOPES: "openid,profile,email,groups,offline_access"
+
+authenticate:
+  # (This we have set in dex's static client also remember! should be same)
+  redirectUrl: "https://authenticate.YOURDOMAIN.dev/oauth2/callback"
+
+  idp:
+    provider: oidc
+    clientID: pom
+    clientSecret: pomerium
+    # (your dex url)
+    url: http://dex.YOURDOMAIN.dev
+    scopes: "openid profile email groups offline_access"
+    # (for group based access policy)
+    serviceAccount: "pomerium-authenticate"
+
+ingress:
+  enabled: true
+  authenticate:
+    name: ""
+  secretName: ""
+  secret:
+    name: ""
+    cert: ""
+    key: ""
+  tls:
+    hosts: []
+  hosts: []
+  annotations:
+    kubernetes.io/ingress.class: nginx
+    kubernetes.io/ingress.allow-http: "true"
+
+resources:
+  limits:
+    cpu: 150m
+    memory: 100Mi
+  requests:
+    cpu: 100m
+    memory: 100Mi
+
+```
+
+