Implement Steam login functionality with OpenID integration

api/Authenticator.api

@@ -13,6 +13,28 @@ type (
 	PingResp {
 		ok bool `json:"ok"`
 	}
+	// Steam Login Types
+	SteamLoginInitReq  {}
+	SteamLoginInitResp {
+		RedirectUrl string `json:"redirectUrl"`
+	}
+	SteamLoginCallbackReq {
+		OpenidMode          string `form:"openid.mode"`
+		OpenidNs            string `form:"openid.ns"`
+		OpenidOpEndpoint    string `form:"openid.op_endpoint"`
+		OpenidClaimedId     string `form:"openid.claimed_id"`
+		OpenidIdentity      string `form:"openid.identity"`
+		OpenidReturnTo      string `form:"openid.return_to"`
+		OpenidResponseNonce string `form:"openid.response_nonce"`
+		OpenidAssocHandle   string `form:"openid.assoc_handle"`
+		OpenidSigned        string `form:"openid.signed"`
+		OpenidSig           string `form:"openid.sig"`
+	}
+	SteamLoginCallbackResp {
+		Success bool   `json:"success"`
+		SteamId string `json:"steamId,omitempty"`
+		Message string `json:"message,omitempty"`
+	}
 )
 
 @server (
@@ -25,5 +47,19 @@ service Authenticator {
 	)
 	@handler pingHandler
 	get /ping (PingReq) returns (PingResp)
+
+	@doc (
+		summary:     "Initiate Steam login"
+		description: "Redirects user to Steam OpenID login page"
+	)
+	@handler steamLoginInitHandler
+	get /steam/login (SteamLoginInitReq) returns (SteamLoginInitResp)
+
+	@doc (
+		summary:     "Steam login callback"
+		description: "Handles the callback from Steam after user authentication"
+	)
+	@handler steamLoginCallbackHandler
+	get /steam/callback (SteamLoginCallbackReq) returns (SteamLoginCallbackResp)
 }